UKHillwalking Article - Twyn Llech and the Welsh – English border

UKHillwalking Article

UKHillwalking recently published an article on the research and survey of Twyn Llech and its summit position in relation to that of the border between Wales and England.  The original article and a link to it on the UKHillwalking website appear below.

Will England Reclaim its Share of a Welsh Mountain?

It's the high point near where the Welsh-English border runs over the Black Mountains, but there all certainty ended. Should it properly be called Black Mountain or Twyn Llech? And which country could rightfully lay claim to the summit? Following research by two independent surveyors, Myrddyn Phillips assisted by Mark Trengove, the mystery surrounding one of the most visited hills in South Wales has finally been cleared up... with a surprising conclusion.

Mark and I are both keen hill walkers with a common interest in hill bagging and the classification of hills. This particular hill was of interest, as its summit position and the location of the border between England and Wales, in relation to the summit, has been under debate. Was the summit on the Welsh side of the border and therefore could the hill be claimed as being Welsh, or was it in fact English? Our aim was to determine where the summit of the hill is positioned, measure its height and plot the course of the border between Wales and England as it crosses the summit plateau.

Twyn Llech

The Name

Rising above the Vale of Ewyas on its Welsh side, and the upper Olchon Valley on its English side, the hill is known by many as  Black Mountain; however research suggests that it was supplanted by early hill-list compilers from the old ridge name given to the main easterly spur of this hill range, and does not apply to the hill itself. This easterly ridge is now known as the 'Hatterrall Ridge' after its southerly outlier, Hatterrall Hill.

Enquiries with the local farming community unearthed the feature name of 'The thieves' stone'. This name was given by David Gains who farms in the Olchon Valley. David explained: 'It's hanging out on a slope, straight on top of the ridge, just on the Welsh side and about 3-4ft wide'. He first heard of this name from his father, who passed on a saying: 'If a sheep grazed the land around the stone and kept by the thieves' stone it would never get maggots'.

This name still appears on contemporary Ordnance Survey maps in its Welsh form of Llech y Lladron, and is given to a rock outcrop on the upper northerly section of the hill.

This and the name of Twyn Llech are the two main named features on this hill, and it is the latter that many know as this hill's referred to Welsh name, which can be translated as 'hill of the stone (or crag)'. This name still appears on Ordnance Survey maps positioned to the west of its summit. Therefore for the remainder of this article we'll refer to the hill as Twyn Llech.

Llech y Lladron

The Hill

Twyn Llech is positioned in the Black Mountains in the south-eastern part of Wales. This hill range has four main extended ridges oriented in a north-west to south-east direction, and Twyn Llech is the highest point of the most easterly of these main ridges.

The hill comprises grass and heather with a base of peat; it is not dramatic in nature but is a great bulk of a hill. The high point is situated toward the northerly section of the main easterly ridge, which extends for approximately 15km. It has two main recognised and individual summits on it, one of which is Twyn Llech and the second the southerly outlier Hatterrall Hill.

There are two significant marker lines on contemporary Ordnance Survey maps that follow the course of this easterly ridge. One is a public right of way that designates part of the Offa's Dyke long distance footpath, and the other is the land border between Wales and England. These are positioned next to one another on the maps. As the summit of the hill is positioned to the west of the ridge path, it has generally been accepted that it is therefore in Wales.

Part of the main eastern ridge

Research

Prior to visiting the hill I conducted extensive research into the position of the border between Wales and England. My hope was to find a written document that gives detail of the position of this land boundary, and especially for the course that it takes over the main easterly ridge of the Black Mountains.

A number of individuals, public bodies and organisations were contacted including the Powys Archives, Powys County Council, National Library of Wales, Longtown Historical Society, Ewyas Study Group, Hereford Record Office, Brecon History Society, Clwyd Powys Archaeological Trust, Hereford Border Authorities, Electoral Services, Boundary Commission, Ordnance Survey, HMSO, Electoral Commission, local historians and the Senedd. None of them could either supply or give information on any form of written document relating to where the land border between Wales and England is positioned. In fact many said that such a document did not exist. The only organisation that gave any indication as to where this border is positioned was the Ordnance Survey, and they simply instructed me to consult their maps.

The Summit

The summit area of this hill comprises a broad ridge of grass and heather with a base of peat. It is relatively flat. However, Twyn Llech has a distinguishable rise on the northerly part of this land, and a dip that leads south to another slight rise approximately 350 metres away, with the northerly high point being relatively easy to distinguish and the southerly high point comprising land that slightly undulates.

These two rises roughly match map detail. The Ordnance Survey give a 703m spot height on their contemporary 1:50,000 Landranger and 1:25,000 Explorer maps, positioned in the southerly part of a 700m continuous contour ring at SO 25586 35010. Harvey maps give a 706m spot height on their 1:40,000 Offa's Dyke South map which is positioned in the northerly part of a 705m continuous contour ring.

First on-site visit

This concentrated on determining the height and position of the northerly high point and its counterpart to the south. This was conducted during an extended walk I completed, taking in a number of other hills. This also prioritised another hill to the south that was surveyed as having less that 15m of drop and which is currently still listed as a Nuttall. The conditions for each survey were excellent with good visibility and little breeze.

The results of these two surveys are:

Northerly high point: 703.639m (converted to OSGM15) at SO 25520 35383

Southerly high point: 702.721m (converted to OSGM15) at SO 25572 35032

A Trimble GeoXH 6000 GNSS receiver was used to determine the height of Twyn Llech and with a 0.9m difference in height there was confidence that the northerly point is where the summit of Twyn Llech is positioned. As the southerly land undulates a second survey to give correlation and confirmation was sought, and the opportunity to do so came nine months later.

The Border

The second on-site visit gave Mark and I the opportunity to plot the course of the land border on the ground as it passes over the summit plateau of Twyn Llech. To do this we used a Garmin GPS Map 64s hand-held device that has access to the Ordnance Survey 1:50,000 mapping. By following the course of the border we determined that it was consistently positioned to the east of the flagged ridge path, and the path itself is also positioned to the east of the summit of both the northerly and southerly points. Having determined where the border lay according to 1:50,000 map detail, we paced from its position to where the Trimble was set up on the northerly summit and its southerly counterpart, with the former being 50 metres and the latter being 45 metres in distance. Therefore, according to contemporary Ordnance Survey 1:50,000 mapping, the summit of Twyn Llech is in Wales.

However sometimes things aren't as simple as they appear...

The second on-site visit had two aims. Firstly we wanted to determine the position of the land border according to Ordnance Survey 1:50,000 mapping, and secondly to take further data sets with the Trimble GeoXH 6000 from the northerly and southerly positions. The conditions for each survey were again ideal with good visibility and not a breath of breeze. The Trimble was placed on a rucksack, which was used as an improvised tripod to give elevation above its immediate surrounds. Respective measurement offsets were taken between its internal antenna and the ground below.

The results of these three further surveys appear below:

Northerly high point: 703.656m (converted to OSGM15) at SO 25520 35383

Southerly high point: 702.787m (converted to OSGM15) at SO 25558 35018

Southerly high point: 702.699m (converted to OSGM15) at SO 25566 35054

These results show excellent correlation with the first set of survey data and confirm that the northerly point is where the summit of Twyn Llech is positioned.

OS Six-Inch map published in 1887 that gives the border as the 'Watershed'

The Ordnance Survey Base Map

Our on-site visit had confirmed where the summit of Twyn Llech is positioned and had given the hill an accurate height. We now compared our findings to the series of Ordnance Survey Six-Inch maps.

For many years the Ordnance Survey Six-Inch map was considered their base map. This was the map for information to be fed onto. The scale was superseded in the 1950s by the 1:10,000 series of maps and was available as sheets until the 1980s when these maps were digitised. The Six-Inch map is still one of the best for giving detail, either numeric or positional, and it was this map that I turned to.

I consulted the series of Six-Inch maps and looked at detail surveyed in 1887 and published in the same year. The land border between Wales and England appears on this map as a split black line, as it does on the publicly available scales of the 1:50,000 and 1:25,000 maps. However, the line of this border on the Six-inch base map has one extremely important word against it - 'Watershed'. The word 'Watershed' also appears beside this border on the Ordnance Survey Vector Map Local that is hosted on the Geograph website and entitled the Interactive Coverage Map. Therefore this word and its implication have remained in the system of Ordnance Survey mapping for over 130 years.

Ordnance Survey Consultation

As there was discrepancy between our on-site findings using the 1:50,000 mapping and the Six-Inch and Vector Map Local maps the Ordnance Survey were consulted and they kindly forwarded the following information:

"Ordnance Survey is not directed by the Ordnance Survey Act 1841 or any other Act to show National boundaries, although they are shown on certain scales of mapping (1:50k / Landranger, does depict National Boundaries between England-Wales, England-Scotland). In OS's most detailed mapping product OS MasterMap the Welsh / English border is located accurately and correctly it is displayed as a County/UA Boundary.

"OS's 1:25k and 1:50k leisure maps are purely contextual to provide a navigational guide to the landscape. Given their scale, these maps should never be used for measuring and surveying purposes. Our leisure maps are derived from the accurate large-scale data but are generalised for clarity, therefore not every feature is shown in the same position as the source data, and we are satisfied with how they currently depict the location of the Welsh English border."

MasterMap is the Ordnance Survey digitised mapping which receives upwards of 10,000 individual updates per day, and as its name implies, this is the master map for Ordnance Survey data.

I was advised by Ordnance Survey that the placement of the border on MasterMap is 12 metres to the east of the grid coordinates I supplied them for the summit of Twyn Llech, meaning that MasterMap places the summit of this hill in Wales.

Boundary Commission for Wales Consultation

After consultation with Ordnance Survey I was advised to contact the Boundary Commission for Wales. If a change in border placement is required it is this organisation that would initiate it. They told me:

"There is no legal mechanism for reviewing the boundary between England and Wales. The boundary is fixed and would require primary legislation to develop a mechanism to make a change to it. The England-Scotland boundary does have such a mechanism and the review is performed jointly by the English and Scottish Boundary Commissions.

"As far as the Commission is concerned the boundary provided by Ordnance Survey, particularly that in its MasterMap product, is the definitive boundary.

"With regard to the specific area to which you referred, I confirm that it is the convention of this Commission that if we were to draw a boundary that it would follow either the top of a ridge-line to its peak or the bottom of a valley depending on the circumstance; where we are not following another easily identifiable boundary (road, railway line, centre of a river, etc.). It may be that when the boundary was originally drawn at the larger scale that that was the intention. We have no records which would ascertain that intention."

Conclusion

My conclusion from the research and survey I've conducted is that the border should be moved and placed on MasterMap going through the summit of Twyn Llech and that primary legislation should be initiated to instigate the mechanism required for such a change. This is based on the convention the Boundary Commission for Wales would adopt and the evidence that the border followed the watershed on this hill's summit plateau on selective Ordnance Survey maps for over 130 years. It is also based on the simple fact that it is the natural course of any boundary on an open mountain such as Twyn Llech to follow the ridge crest which is also the watershed. The simple fact of the matter is that no one had ever surveyed this hill for where its summit is positioned prior to our visit, therefore the border placement on MasterMap although very close to the summit is still 12 metres from it and in all probability was placed to the best of the respective cartographer's presumption of where the watershed is positioned.

So which nation rightly lays claim to the summit of Twyn Llech? I'd say both. If the reinstated course of the border is accepted then it can be considered a dual national hill.

Myrddyn Phillips with Mark Trengove

For the original article published on the UKHillwalking website

Grough Article - Twyn Llech and the Welsh – English border

Grough Article

Grough recently published an article on the research and survey of Twyn Llech and its summit position in relation to that of the border between Wales and England.  The original article and a link to it on the Grough website appear below.

Hill sleuth Myrddyn Phillips's border research suggests Wales should shrink a little

Myrddyn Phillips, Guest contributor
Wednesday 06 March 2019 12:01 AM GMT

A Welshman who is a keen hillwalker and amateur surveyor believes research demonstrates his home nation should shrink a little and England could be expanded.

Myrddyn Phillips, with help from fellow walker Mark Trengove, spent months researching and surveying a hill that forms the boundary between the two nations.

The view from England of the main ridge separating it from Wales

The popular hill in south Wales has finally had the position of its summit confirmed, along with its relation to the land border between Wales and England, with possible consequences for the boundary between the two nations.

Here, the pair advance their case for a review of the Wales-England border on the south-eastern boundary of the Brecon Beacons, and detail the months of research that led them to their conclusion.

The hill rises above the Vale of Ewyas on its Welsh side, and the upper Olchon Valley on its English side. Even its name is under debate; is it the Welsh Twyn Llech or the English Black Mountain?



The Name

The hill is known by many as Black Mountain. However, research into the use of this name suggests that it was supplanted by early hill-list compilers from the old ridge name given to the main easterly spur of this hill range, and does not apply to the hill itself. This easterly ridge is now known as the Hatterrall Ridge after its southerly outlier, Hatterrall Hill.

Extensive local enquiries by Myrddyn Phillips with the local farming community unearthed the feature name of the Thieves’ Stone. This name was given by David Gains who farms in the Olchon Valley which is situated on the English side of the hill. Mr Gains said: “It’s hanging out on a slope, straight on top of the ridge, just on the Welsh side and about 3-4ft wide.”

He was asked when and how he had first heard of this name. He replied that his father had told him, saying that he’d heard: “If a sheep grazed the land around the stone and kept by the Thieves’ Stone it would never get maggots.”

This feature name still appears on contemporary Ordnance Survey maps in its Welsh form of Llech y Lladron, and is given to a rock outcrop on the upper and northerly section of this hill.

This and the name of Twyn Llech are the two main named features on this hill, and it is the latter that many know as this hill’s referred-to Welsh name, which can be translated as ‘hill of the stone or crag’. This name still appears on Ordnance Survey maps positioned to the west of its summit. Therefore for the remainder of this article we’ll refer to the hill as Twyn Llech.

The Hill

Twyn Llech is positioned in the Black Mountains range of hills, situated in the south-eastern part of Wales. This hill range has four main extended ridges oriented in a north-west to south-east direction, and Twyn Llech is the highest point of the most easterly of these main ridges.

Twyn Llech, which forms part of the border between Wales and England

The hill comprises grass and heather with a base of peat. It is not dramatic in nature but is a great bulk of a hill. The high point is situated toward the northerly section of the main easterly ridge, which extends for approximately 15km (over nine miles). It has two main recognised and individual summits on it, one of which is Twyn Llech and the second the southerly outlier Hatterrall Hill.

There are two significant marker lines on contemporary Ordnance Survey maps that follow the course of this easterly ridge. One is a public right of way that designates a part of the Offa’s Dyke long-distance footpath, and the other is the land border between Wales and England. Both the public footpath and the land border are positioned next to one another on contemporary Ordnance Survey maps. As the summit of the hill is positioned to the west of the ridge path, it has generally been accepted that it is therefore in Wales, and over recent years the ridge path has been flagged in many sections to reduce encroaching erosion.

Introduction

Mark and I are both keen hillwalkers with a common interest in hill-bagging and the classification of hills. This particular hill was of interest, as its summit position and the location of the border between England and Wales, in relation to the summit, has been under debate. Was the summit of the hill on the Welsh side of the border and therefore could the hill be claimed as being Welsh, or was it on the English side and could the hill be claimed as being English? Our aim was to determine where the summit of the hill is positioned, measure its height and plot the course of the border between Wales and England as it crosses the summit plateau of Twyn Llech.

Research

Before visiting the hill I conducted extensive research in to the position of the border between Wales and England. My hope was to find a written document that gives detail of the position of this land boundary, and especially for the course that it takes over the main easterly ridge of the Black Mountains.

A number of individuals, public bodies and organisations were contacted including the Powys Archives, Powys County Council, National Library of Wales, Longtown Historical Society, Ewyas Study Group, Hereford Record Office, Brecon History Society, Clwyd Powys Archaeological Trust, Hereford Border Authorities, Electoral Services, Boundary Commission, Ordnance Survey, HMSO, Electoral Commission, local historians and the Senedd.

None of these individuals and organisations could either supply or give information on any form of written document to where the land border between Wales and England is positioned. In fact many said that such a document did not exist. The only organisation that gave any indication as to where this border is positioned was the Ordnance Survey, and they instructed me to consult their maps, as these would show the position of the border.

The summit

The summit area of this hill comprises a broad ridge of grass and heather with a base of peat. It is relatively flat in nature. However, Twyn Llech has a distinguishable rise on the northerly part of this land, and a dip that leads south to another slight rise approximately 350m away, with the northerly high point being relatively easy to distinguish and the southerly high point comprising land that slightly undulates.

A distant Mark Trengove stands on the northern summit

These two rises, one to the north and one to the south, roughly match map detail. The Ordnance Survey give a 703m spot height on their contemporary 1:50,000 Landranger and 1:25,000 Explorer maps, positioned in the southerly part of a 700m continuous contour ring at grid reference SO 25586 35010. Harvey maps give a 706m spot height on their 1:40,000 Offa’s Dyke South map which is positioned in the northerly part of a 705m continuous contour ring.

First on-site visit

The first on-site visit concentrated on determining the height and position of the northerly high point and its counterpart to the south. This was conducted during an extended walk I completed, taking in a number of other hills. This also prioritised another hill to the south that was surveyed as having less that 15m of drop and which is currently still listed as a Nuttall. The conditions for each survey were excellent with good visibility and little breeze.

The results of these two surveys are:

• Northerly high point: 703.639m (converted to OSGM15) at SO 25520 35383
• Southerly high point: 702.721m (converted to OSGM15) at SO 25572 35032

A Trimble GeoXH 6000 GNSS receiver was used to determine the height of Twyn Llech and with a 0.9m difference in height there was confidence that the northerly point is where the summit of Twyn Llech is positioned. As the southerly land undulates a second survey to give correlation and confirmation was sought, and the opportunity to do so came nine months later.

The border

The second on-site visit gave Mark and me the opportunity to plot the course of the land border on the ground as it passes over the summit plateau of Twyn Llech. To do this we used a Garmin GPS Map 64s hand-held device that has access to the Ordnance Survey 1:50,000 mapping. By following the course of the border we determined that it was consistently positioned to the east of the flagged ridge path, and the path itself is also positioned to the east of the summit of both the northerly and southerly points. Having determined where the border lay according to 1:50,000 map detail, we paced from its position to where the Trimble was set-up on the northerly summit and its southerly counterpart, with the former being 50m and the latter being 45m in distance. Therefore, according to contemporary Ordnance Survey 1:50,000 mapping, the summit of Twyn Llech is in Wales.

However sometimes things aren’t as simple as they appear.

Second on-site visit

The second on-site visit had two aims. Firstly we wanted to determine the position of the land border according to Ordnance Survey 1:50,000 mapping, and secondly to take further data sets with the Trimble GeoXH 6000 from the northerly and southerly positions. The conditions for each survey were again ideal with good visibility and not a breath of breeze. The Trimble was placed on a rucksack, which was used as an improvised tripod to give elevation above its immediate surrounds. Respective measurement offsets were taken between its internal antenna and the ground below.

The flagged and maintained path leading to the northern high-point

The results of these three further surveys are:

• Northerly high point: 703.656m (converted to OSGM15) at SO 25520 35383
• Southerly high point: 702.787m (converted to OSGM15) at SO 25558 35018
• Southerly high point: 702.699m (converted to OSGM15) at SO 25566 35054

These results show excellent correlation with the first set of survey data and confirm that the northerly point is where the summit of Twyn Llech is positioned.

Map comparison

Our on-site visit had confirmed where the summit of Twyn Llech is positioned and had given the hill an accurate height. It also seemed to confirm that the border between Wales and England is approximately 50m to the East of the summit and therefore the high point of the hill is in Wales. However, to confirm the position of the border we wanted to compare the other publicly available scale of Ordnance Survey map: the 1:25,000 Explorer series and then compare these details against the series of Ordnance Survey six-inch maps.

As the 1:25,000 Explorer map gave the position of the border as no more than 10-15m from the summit of the hill, compared to the 50m of the 1:50,000 Landranger map we now turned to the series of six-inch maps.

The Ordnance Survey base map

For many years the Ordnance Survey six-inch map was considered their base map. This was the map for information to be fed on to. The scale was superseded in the 1950s by the 1:10,000 series of maps and was available as sheets until the 1980s when these maps were digitised. The six-inch map is still one of the best for giving detail, either numerical or positional.

A detail from the six-inch map, with the word 'watershed' marked against the border

We consulted the series of six-inch maps and looked at detail surveyed in 1887 and published in the same year. The land border between Wales and England appears on this map as a split black line, as it does on the publicly available scales of 1:50,000 and 1:25,000 maps. However, the line of this border on the six-inch map has one extremely important word placed against it: watershed.

The word watershed also appears beside this border on the Ordnance Survey Vector Map Local that is hosted on the Geograph website and entitled the Interactive Coverage Map. Therefore this word and its implication have remained in the system of Ordnance Survey mapping for more than 130 years.

Ordnance Survey consultation

As there was discrepancy between our on-site findings using the 1:50,000 mapping and the six-inch and Vector Map Local maps the Ordnance Survey were consulted and they kindly forwarded the following information.

“Ordnance Survey are not directed by the Ordnance Survey Act 1841 or any other Act to show national boundaries, although they are shown on certain scales of mapping (1:50k/Landranger, does depict national boundaries between England-Wales, England-Scotland). In OS’s most detailed mapping product OS MasterMap the Welsh-English border is located accurately and correctly. It is displayed as a County/UA boundary.

“OS’s 1:25k and 1:50k leisure maps are purely contextual to provide a navigational guide to the landscape. Given their scale, these maps should never be used for measuring and surveying purposes. Our leisure maps are derived from the accurate large-scale data but are generalised for clarity, therefore not every feature is shown in the same position as the source data, and we are satisfied with how they currently depict the location of the Welsh-English border.”

The OS MasterMap is the Ordnance Survey digitised mapping which receives upwards of 10,000 individual updates per day and as its name implies, this is the master map for Ordnance Survey data.

I was advised by Ordnance Survey that the placement of the border on MasterMap is 12m to the East of the grid coordinates I supplied them for the summit position of Twyn Llech, and this means that MasterMap places the summit of this hill in Wales.

Boundary Commission for Wales consultation

After consultation with Ordnance Survey I was advised to contact the Boundary Commission for Wales. It is this organisation that if a change in border placement is required would instigate it. This organisation kindly forwarded the following:

The equipment in operation during the third survey of the southern point

“There is no legal mechanism for reviewing the boundary between England and Wales. The boundary is fixed and would require primary legislation to develop a mechanism to make a change to it. The England-Scotland boundary does have such a mechanism and the review is performed jointly by the English and Scottish Boundary Commissions.

“As far as the commission is concerned the boundary provided by Ordnance Survey, particularly that in its MasterMap product, is the definitive boundary.

“With regard to the specific area to which you referred, I confirm that it is the convention of this commission that if we were to draw a boundary that it would follow either the top of a ridge-line to its peak or the bottom of a valley depending on the circumstance, where we are not following another easily identifiable boundary (road, railway line, centre of a river, etc). It may be that when the boundary was originally drawn at the larger scale that that was the intention. We have no records which would ascertain that intention.”

Conclusion

My conclusion from the research and survey I have conducted with the assistance of Mark Trengove is that the border should be moved and placed on MasterMap going through the summit of Twyn Llech and that primary legislation should be initiated to instigate the mechanism required for such a change.

This is based on the convention the Boundary Commission for Wales would adopt and the evidence that the border followed the watershed on this hill’s summit plateau on selective Ordnance Survey maps for more than 130 years.

Myrddyn Phillips

It is also based on the fact that it is the natural course of any boundary on an open mountain such as Twyn Llech to follow the ridge crest which is also the watershed. The simple fact of the matter is that no one had ever surveyed this hill for where its summit is positioned prior to our visit. Therefore, the border placement on MasterMap although very close to the summit is still 12m from it and in all probability the cartographer who placed it was doing so to where they thought the watershed lay.

Myrddyn Phillips with Mark Trengove

For the original article published on the Grough website

Determining the position of the Welsh – English border relative to the summit of Twyn Llech (SO 255 353)

Before detailing our on-site adventures, it may be prudent to briefly concentrate on the name of this hill.

The hill is known by many as Black Mountain; however research in to the use of this name suggests that it was supplanted by early hill list compilers from the old ridge name given to the main easterly ridge of this hill range and does not apply to the hill itself. 

Extensive local enquiries with the farming community unearthed the feature name of the thief’s stone; this name was given by David Gains, who farms from the Olchon Valley, situated on the English side of the hill.  This feature name still appears on contemporary Ordnance Survey maps in its Welsh form of Llech y Lladron.  It is given to a rock outcrop on the upper and northerly part of this hill.  This and the name of Twyn Llech are the two main named features on this hill, and it is the latter that many know as this hill’s referred to Welsh name.  The name of Twyn Llech, which can be translated as hill of the stone (or crag), still appears on Ordnance Survey maps and is positioned to the west of its summit.  Therefore, for the remainder of this article this hill is referred to as Twyn Llech.

Mark on Llech y Lladron; the thief's stone 

Twyn Llech is positioned in the Black Mountains range of hills which are situated in the south-eastern part of Wales.  This hill range has four main extended ridges oriented in a north-west to south-east direction.  Twyn Llech is the highest point of the most easterly of these main ridges.

Twyn Llech (SO 255 353)

The hill comprises grass and heather with a base of peat; it is not dramatic in nature but is a great bulk of a hill.  Its high point is situated toward the northerly section of the main easterly ridge, which extends for approximately 15km (over nine miles).  It has two main recognised and individual summits on it, one of which is Twyn Llech and the second the southerly outlier of Hatterrall Hill (SO 308 256).

Part of the main easterly ridge of the Black Mountains

Our intention was to determine the summit position of Twyn Llech, survey this point for absolute height and discover where, in relation to this point, the border between Wales and England is positioned.  If clarity could be given to the above, we hoped this would reveal whether the summit of Twyn Llech is positioned in Wales or in England, or whether it is a Dual National Hill. 

The summit of Twyn Llech was surveyed over two days, each nine months apart.  Before detailing the first survey of this hill, we need to detail the map height and classifications of this hill.

Twyn Llech is given a 703m summit spot height on contemporary Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps.  This is positioned in the southerly part of a 700m continuous contour ring at SO 25586 35010.  However, Harvey maps give a 706m summit spot height on their 1:40,000 Offa’s Dyke South map.  This is positioned in the northerly part of a 705m continuous contour ring. 

Extract from the Ordnance Survey 1:25,000 Explorer map

Extract from Harvey maps

Many peat based moorland hills have relatively flat summit areas, and Twyn Llech is no exception.  The spot heights on Ordnance Survey and Harvey maps indicate a southerly high point and a northerly high point, each separated by approximately 350 metres.  This is so on the ground, with the northerly high point more distinguishable than its southerly counterpart which is undulating in nature.

This hill is classified in many categories as befits its prominence which is over 150m, these are; Marilyn, Hump, Tump and Twmpau, and as its height exceeds 700m it is also classified as a Simm, Hewitt, Nuttall and Uchaf.  It is also included in many past hill lists which are now viewed as being historic.  Twyn Llech is also classified as a Historic County Top, current County/UA Top and an Administrative County Top.

I’d visited Twyn Llech on 18 occasions prior to the first survey of its summit, with the majority of these approaching the high point of the hill from the south.  As I walked up the broad southerly ridge of this hill I always thought that land to the north of where the Ordnance Survey 703m spot height appears to be slightly higher, but I had no instrumentation to prove this.

The first survey of Twyn Llech took place on the 28^th September 2017 whilst on an extended walk, taking in a number of hills.  The conditions for the survey were excellent with good visibility and little breeze.

I approached from the direction of Hay Bluff (SO 244 366) and found the northerly high point relatively easy to pinpoint.  The hill was surveyed using a Trimble GeoXH 6000 GNSS receiver.  The first survey was conducted between 12.34pm – 12.39pm, with five minutes of data gathered. The area surrounding the summit consists of moor grass and heather.

The position of the southerly high point is harder to determine, as its land undulates.  It is of similar nature to its northerly counterpart and consists of moor grass and heather.  I chose a narrow path leading from a small cairn placed beside the flagged ridge path for the Trimble set-up position and again gathered five minutes of data between 12.56pm – 1.01pm.

The results of these two surveys appear below:

Northerly high point:  703.639m (converted to OSGM15) at SO 25520 35383

Southerly high point:  702.721m (converted to OSGM15) at SO 25572 35032

First survey at the northerly high point - the summit of Twyn Llech

First survey at the southerly point

With a 0.9m difference in height I was confident that the northerly point is where the summit of Twyn Llech is positioned, but as the land where the southerly point undulates I wanted to revisit and take further data sets to provide confirmation of this first survey.  The opportunity to do so came when Mark suggested two walks; the first to the summit of Hatterrall Hill, and the second to the summit of Twyn Llech.  As Mark knew of the first survey result, he wanted to visit the northerly high point and confirm his Marilyn ascent, but he was also enthusiastic to pinpoint where the Welsh - English border is positioned in relation to the summit of this hill.

Prior to the visit I had conducted extensive research with the aim being to consult any written text that gives details of where the border between Wales and England is positioned and specifically for the land border passing over the Black Mountains hill range.  I had contacted a number of individuals, public bodies and organisations including the Powys Archives, Powys County Council, National Library of Wales, Longtown Historical Society, Ewyas Study Group, Hereford Record Office, Brecon History Society, Clwyd Powys Archaeological Trust, Hereford Border Authorities, Electoral Services, Boundary Commission, Ordnance Survey, HMSO, Electoral Commission, local historians and the Senedd.  None of these individuals and organisations could either supply or give information on any form of written document to where the land border between Wales and England is positioned.  In fact many said that such a document did not exist.  The only organisation that gave any indication of where this border is positioned was the Ordnance Survey, and they instructed me to consult their maps, as these would show the position of the border.

We visited Twyn Llech in the early evening of 12^th July 2018, approaching from the Gospel Pass car park via the summit of Hay Bluff.  As we reached steepening ground heading toward the hill’s summit plateau, we visited the rock outcrop named Llech y Lladron.  Once back on the main ridge path Mark activated his Garmin and started to plot on the ground where the 1:50,000 map positions the border.  This was consistently to the east of the flagged ridge path which forms a part of the Offa’s Dyke long distance footpath. 

Once at the northerly high point the Trimble was set up to gather data.  We checked each high point for best position and the measurement offset between the internal antenna in the Trimble and the ground at the base of the rucksack which is used as an improvised tripod for many of the Trimble surveys.  Meanwhile Mark also undertook the task of determining where the land border, according to the Ordnance Survey 1:50,000 map, exists on the ground as it crosses the summit ridge of Twyn Llech.  He used a Garmin GPSMap 64s hand-held device to do this, as it is uploaded with the Ordnance Survey 1:50,000 Landranger mapping.  This can be examined in fine detail on the screen with the dotted line of the border followed on the hill.

Second survey at the northerly high point - the summit of Twyn Llech

We paced out the distance between what proved to be the summit of the hill and the flagged path.  This came to approximately 12 metres, and from here we continued eastward to where the 1:50,000 map places the border.  It was a further 38 metres to this point, totalling 50 metres in all from the summit to the border, according to the 1:50,000 Landranger map.

We repeated this process for the southerly high point and found the Trimble position for the higher of the two surveys conducted to be 15 metres from the flagged path and a further 30m to the land border, according to the 1:50,000 map.  This totalled 45 metres in all from the Trimble set-up position to the border.

Second survey at the southerly point

The second survey of Twyn Llech was again conducted in excellent conditions with good visibility and not a breath of breeze.  A ten minute data set was gathered from each of three points, the first on the northerly high point and two from the southerly point.  The survey of the northerly high point was conducted between 6.13pm – 6.23pm and the grid coordinates produced from post processing matched those from the first survey of this same point in September 2017; SO 25520 35383.

As the ground at the southerly highpoint slightly undulates, I wanted to take a further two data sets from here, but in different positions to where the Trimble was placed during the September 2017 survey.  I easily found the point where the Trimble had previously been set up on the narrow path that leads west from the small cairn beside the flagged ridge path, and with Mark’s assistance, we studied the lay of land and chose two further points.  Each of these was of similar height to the narrow path and each we considered as potential highpoints for this southerly land.  The Trimble GeoXH 6000 gathered two further data sets from these points between 6.43pm – 6.53pm and 6.58pm – 7.08pm respectively. 

Third survey at the southerly point

Over two days, almost nine months apart, two data sets were gathered from the northerly high point and three from land comprising the southerly high point, with all Estimated Accuracies given as 5-15cm: 100.00% and the Standard Deviation as 0.0m, meaning all data sets are good.

The results of these three further surveys appear below:

Northerly high point:  703.656m (converted to OSGM15) at SO 25520 35383

Southerly high point:  702.787m (converted to OSGM15) at SO 25558 35018

Southerly high point:  702.699m (converted to OSGM15) at SO 25566 35054

These results show excellent correlation with the first set of survey results produced in September 2017 with the exact same position for the Trimble on the northerly high point with the two surveys; 703.639m and 703.656m only being 0.017m apart.

Three positional surveys were conducted on the southerly high point, all within a grid approximately 14 metres by 36 metres.  Their results; 702.721m, 702.787m and 702.699m are within 0.088m of one another, confirming that the southerly high point is lower than the northerly high point.  Therefore the summit of Twyn Llech is positioned at SO 25520 35383 and its height given by the Trimble GeoXH 6000 is 703.6m (average of two summit surveys).

However, what of the border between Wales and England and does this result confirm that the summit of Twyn Llech is positioned in Wales as the Ordnance Survey 1:50,000 map implies?

Our on-site visit had confirmed where the summit of Twyn Llech is positioned and had given the hill an accurate height.  We now compared our findings to the series of Ordnance Survey Six-Inch maps.

For many years the Ordnance Survey Six-Inch map was considered their base map.  This was the map for information to be fed onto.  The scale was superseded in the 1950s by the 1:10,000 series of maps and was available as sheets until the 1980s when these maps were digitised.  The Six-Inch map is still one of the best for giving detail, either numerical or positional, and it was this map that we turned to.

We consulted the series of Six-Inch maps and looked at detail surveyed in 1887 and published in the same year.  The land border between Wales and England appears on this map as a split black line, as it does on the publicly available scales of 1:50,000 and 1:25,000 maps.  However, the line of this border on the Six-Inch map has one extremely important word placed against it – ‘Watershed’.

Extract from the Ordnance Survey Six-Inch map published in 1887 with the all-important word 'Watershed' following the course of the border

The word ‘Watershed’ also appears beside this border on the Ordnance Survey Vector Map Local that is hosted on the Geograph website and entitled the Interactive Coverage Map.  Therefore this word and its implication have remained in the system of Ordnance Survey mapping for over 130 years.

Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website and which is entitled the Interactive Coverage Map with the all important word 'Watershed' still appearing

As there was discrepancy between our on-site findings using the 1:50,000 mapping and the Six-Inch and Vector Map Local maps the Ordnance Survey were consulted and they kindly forwarded the following information:

‘Ordnance Survey are not directed by the Ordnance Survey Act 1841 or any other Act to show National boundaries, although they are shown on certain scales of mapping (1:50k / Landranger, does depict National Boundaries between England-Wales, England-Scotland).  In Os’s most detailed mapping product OS MasterMap the Welsh / English border is located accurately and correctly it is displayed as a County/UA Boundary.

‘OS’s 1:25k and 1:50k leisure maps are purely contextual to provide a navigational guide to the landscape.  Given their scale, these maps should never be used for measuring and surveying purposes.  Our leisure maps are derived from the accurate large-scale data but are generalised for clarity, therefore not every feature is shown in the same position as the source data, and we are satisfied with how they currently depict the location of the Welsh English border.’

The OS MasterMap is the Ordnance Survey digitised mapping which receives upwards of 10,000 individual updates per day and as its name implies, this is the master map for Ordnance Survey data.

I was advised by Ordnance Survey that the placement of the border on MasterMap is 12 metres to the east of the grid coordinates I supplied them for the summit position of Twyn Llech, and this means that MasterMap places the summit of this hill in Wales.

After consultation with Ordnance Survey I was advised to contact the Boundary Commission for Wales, it is this organisation that if a change in border placement is required would instigate it.  This organisation kindly forwarded the below:

‘There is no legal mechanism for reviewing the boundary between England and Wales.  The boundary is fixed and would require primary legislation to develop a mechanism to make a change to it.  The England-Scotland boundary does have such a mechanism and the review is performed jointly by the English and Scottish Boundary Commissions.

As far as the Commission is concerned the boundary provided by Ordnance Survey, particularly that in its MasterMap product, is the definitive boundary.

With regard to the specific area to which you referred, I confirm that it is the convention of this Commission that if we were to draw a boundary that it would follow either the top of a ridge-line to its peak or the bottom of a valley depending on the circumstance; where we are not following another easily identifiable boundary (road, railway line, centre of a river, etc.).  It may be that when the boundary was originally drawn at the larger scale that that was the intention.  We have no records which would ascertain that intention’.

My conclusion from the research and survey I have conducted is that the border should be moved and placed on MasterMap going through the summit of Twyn Llech and that primary legislation should be initiated to instigate the mechanism required for such a change.  This is based on the convention the Boundary Commission for Wales would adopt and the evidence that the border followed the watershed on this hill’s summit plateau on selective Ordnance Survey maps for over 130 years.  It is also based on the fact that it is the natural course of any boundary on an open mountain such as Twyn Llech to follow the ridge crest which is also the watershed.  The simple fact of the matter is that no one had ever surveyed this hill for where its summit is positioned prior to our visit, therefore the border placement on MasterMap although very close to the summit is still 12 metres from it and in all probability the cartographer who placed it was doing so to where they thought the watershed lay.

Myrddyn Phillips and Mark Trengove (March 2019)

Grough article detailing the research and survey relating to Twyn Llech and the border   

UKHillwalking article detailing the research and survey relating to Twyn Llech and the border