Trecastle is named after Castle Tump an early 11th-century Normanmotte-and-bailey fortification , built by Bernard de Neufmarche and designed to protect Brecon from attack from the west. Despite this purpose, the area continued to be threatened, with Edward I of England spending three days in Trecastle quelling a revolt in 1295. The old castle name of 'una villa nostra de Lliwel' was changed by the end of the Medieval era to the local name Trecastle, "the town of the castle". The fortification still exists at the east end of the village and the motte is high; the largest of its type inthe National Park. From around the 12th century the Bishop of St David's owned the land to the west of the book and Trecastle was thus used as a staging post en route to the Cathedral. After leaving the stopping point the road is thought to have turned to follow the Roman Road near Y Pigwn. Centuries later, Trecastle was used by coach travellers as a stopping point on the route from Gloucester to Llandovery. In the 19th century Trecastle had eight annual fairs, its own gasworks, two schools, a grainmill, two smithies, 16 shops and numerous pubs. Between 1830 and 1914, Trecastle and Llywel are said to have had two of the most important wool mills in Brecknockshire. The arrival of the railway in Sennybridge meant that Trecastle lost its place as the trading centre for the area. Trecastle is situated on the A40trunk road between Brecon and Llandovery, which largely follows the old coaching route and passes a monument to a coach crash in the 19th century between Trecastle and Llandovery. The village was extended in 1960 to 1970s but maintains its linear pattern. It is now known for its antique trade.
Monuments and buildings
Trecastle's history makes it one of the longest-established Brecknockshire villages, thus the Motte & Bailey is considered an important ancient & medieval monument and the village contains a number of listedGeorgian and Medieval properties. Listed buildings in Trecastle include;
Castle Tump, early 11th-century scheduled CADW ancient monument.
File:Y Pigwm.jpeg|thumb|left|Y Pigwm, Trecastle, Breconshire. Plan of the Roman Marching Camps at Y Pigwm , drawn by William Rees in 1854 Near the village is the site of Y Pigwn. This consists of two overlaying Roman practice marching camps which are on the summit of Trecastle Mountain. They have been described as 'amongst the best-preserved and best-known Roman temporary camps in Wales. The camps were first discovered 1849 and were planned and described by William Rees at the meeting of the Cambrian Archaeological Association at Breconin 1853. Rees also illustrates Bronze Age burial urns which were found by a Mr Holford in nearby burial mounds. The "Y Pigwm" camps are close to the presumed Roman road linking the Roman Forts at Llandovery and Brecon Gaer, and a small Roman fortlet at "Waun Ddu" lies 700m to the West. There are standing stones and a stone circle nearby.
