The ancient commote of Senghenydd (corresponding to the modern hundred of Caerphilly) comprised the mountainous district extending from the ridge of Cefn Onn on the south to Breconshire on the north, being bounded by the rivers Taff and Rumney on the west and east.
Rowland and Harris had been at work fully eighteen months before they met, at a service in Devynock church, in the upper part of Breconshire.
Their highest summit north of the Usk, on the eastern side, where they are known as the Black Mountains, or sometimes the Black Forest Mountains, is Pen y Gader (2624 ft.) between Talgarth and Llanthony, and on the south-west the twin peaks of the Mynydd Du ("Black Mountain") or the so-called Carmarthenshire Vans or Beacons, only the higher of which, Fan Brycheiniog (2632 ft.), is, however, in Breconshire; while the centre of the crescent is occupied by the masses of the Brecknockshire Beacons or Vans (often called the Beacons simply), the highest point of which, Pen y Fan, formerly also known as Cadair Arthur, or Arthur's Chair, attains an altitude of 2910 ft.
There are no traces or record of Breconshire being inhabited before the Neolithic period, but to that period may be ascribed a.
The Usk (56 m.) flows through Breconshire, and joins the Bristol Channel at Newport in Monmouthshire.