Brithdir hamlet is in the north-east of the parish, and covers the area of the parish between Nant Bargod Rhymni and the Rhymney river. The main communities in this hamlet today are Pontlottyn, Tirphil and Brithdir plus that part of Deri east of Nant Bargod Rhymni. This was divided into 19 farms of between 36 and 293 acres, plus two plots of land of 833 acres and 253 acres which had previously been agricultural but which by 1841 was occupied by The Rhymney Iron Company. There was also much land that was common land.
The boundries of the Hamlet in 1750 were given as “it begins where Bargod River goes to Rumney by Aberbargod bridge then along the River Bargod upwards till it comes very near the way upon the common that leadeth from Kevan y Brithdire to Twyn y wayn then directly westward to the three stones in the heath below Twyn y wayn between Merthyr and Gellygare then directly to the east side of Twyn y wayn then directly to Fynnon Gwelliw then to the old water pond in Pant y wayn coal pits then directly to the spring head of a brook called nant y Glaynon then to Pwll llwchmeare then to carn y clyndir or mark ycha then to carn helig then to Rhyd yr Milwr on the river Rymney then along the river Rymney to Aberbargod bridge aforesaid”.
The industrial revolution arrived in Gelligaer in Pontlottyn and this is reflected in the population figures shown below. By 1881 population was no longer recorded by hamlet as their function had all but disappeared.
The farms as recorded in the 1841 tithe schedule are shown below. Many of these names still appear on the modern OS map although now sometimes referring to a village rather than a farm. So we now have Pontlottyn (a village), Ty Newydd (disappeared), Dyffryn farm, Troedrhiwfuwch farm (a village of that name has now gone), Craig-Rhymney farm, Tirphil (a village), Tyla-ddu, Brithdir-uchaf and Brithdir-isaf are now forrested, Troed-y-rhiw Jestyn (a farm), Coed Deri-Newydd (forrested, some of the land is part of the village of Deri), Pen-y-fid Fedw (now forrested) ,Tyr-capel (a farm), Cefn Bach farm, Groes-faen farm (parts of both Cefn Bach and Groes-faen are forrested), Tir Evan Thomas now Plas Milfre, Cefn-y-brithdir (a farm), Brithdir which was also known as Brithdir-ganol has been absorbed into neighbouring farms and the village of Brithdir, Tir-y-ferch-gryno (a farm), Gwaelod-y-brithdir (a farm).
The tithe value has been converted to modern pounds/pence; it gives an indication of the relative values of the farms in 1841.