Mapping Mountains – Significant Name Changes – 200m Twmpau

Mynydd Pant yr Onn (SH 663 000) 

There has been a Significant Name Change to a hill that is listed in the 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Mynydd Pant yr Onn (SH 663 000)

The criteria for the list that this name change applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The hill is adjoined to the Tarren y Gesail group of hills, which are situated in the south-western part of North Wales (Region A, Sub-Region A3), and it is positioned with a minor road to its south and the A493 road farther to its south-east, and has the town of Machynlleth towards the east.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the accompanying Hills to be surveyed sub list under the transposed name of Allt Nantygwenlli, which is a prominent name that appears to the north north-west of the summit on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

Allt Nantygwenlli

270c

SH663000

135

23

During my early hill listing I thought it appropriate to either invent a name for a hill or use a name that appeared near to the summit of the hill on Ordnance Survey maps of the day, with little consideration for the meaning of the name and where it was appropriately applied to.  My preference was to use farm names and put Pen, Bryn or Moel in front of them or as in this instance transpose a prominent name that appears on contemporary Ordnance Survey maps.  This is not a practice that I now advocate as with time and inclination place-name data can be improved either by asking local people or by examining historic documents, through this form of research an appropriate name for the hill can usually be found.                   

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

As the summit of this hill comprises bounded land the details for it were examined on the Tithe map.  The term Tithe map is generally given to a map of a Welsh or English parish or township and which was prepared after the 1836 Tithe Commutation Act.  This act allowed tithes to be paid in cash rather than goods.  The Tithe maps gave names of owners and occupiers of land in each parish and importantly for place-name research they also included the name of enclosed land.  This enclosed land is usually based on a field system, however not every field is given a name, but many are and especially so in Wales. 

Extract from the Tithe map

The enclosed land where the summit of this hill is situated is given the number 270 on the Tithe map, this can be cross referenced against the apportionments; it is these apportionments that give the name of the owner or occupier of the land as well as the name of the land.  The land where the summit of this hill is situated is named as Sheepwalk Pant yr Onn in the apportionments, with the details on the Tithe map appearing in the parish named as Tywyn and in the county named as Merioneth. 

Extract from the apportionments

The intricacies of language and prioritising one in favour of another for listing a hill is fraught with complication, with originating Cymraeg names being anglicised and also originating English names being cymricised, examples such as these are more common in border country and especially so for anglicised forms.  There is no steadfast rule that fits all, but as a standard a name that has its origins in the Welsh language and where this is substantiated by either historic documentation and/or contemporary usage should be prioritised in favour of a contemporary anglicised or English version of the name.  Likewise, if a name exists where an element of it is in English and if this name applies to a hill that is situated in a Welsh speaking part of Wales it is standard practice to use a full Welsh term for the name.  It is also standard practice to use a Welsh name for a hill if another name exists that has originated in a different language.

Therefore, the name this hill is now listed by in the 200m Twmpau is Mynydd Pant yr Onn, and this was derived from the Tithe map, with the language protocol also being used. 

 

The full details for the hill are:

Group:  Tarren y Gesail

Name:  Mynydd Pant yr Onn

Previously Listed Name:  Allt Nantygwenlli   

OS 1:50,000 map:  135

Summit Height:  271.2m (LIDAR) 

Summit Grid Reference:  SH 66362 00021 (LIDAR) 

Bwlch Height:  249.4m (LIDAR) 

Bwlch Grid Reference:  SH 66270 00131 (LIDAR) 

Drop:  21.8m (LIDAR) 

 

Myrddyn Phillips (June 2025)