The Cistercian abbey of Strata Florida was initially founded in 1164 by Robert fitz Stephen, an Anglo-Norman lord. However, patronage of the fledgling community was soon assumed by Rhys ap Gruffudd, prince of the ancient kingship of Deheubarth. Before 1200 an ambitious building programme was engaged and in 1201, the Cistercians took possession of their new church at Strata Florida. It is highly likely that the Abbey was not totally completed by the middle of the thirteenth century. Through the course of the thirteenth century, the Abbey was an ardent supporter of the Welsh cause, occasionally resulting in the hostility of the kings of England. It was at Strata Florida that a copy of Brut y Tywysogyon (Chronicle of the princes) was written, and it was here too that many members of the Deheubarth dynasty of princes were laid to rest. The abbey at Strata Florida suffered damage during the Welsh wars of King Edward I in 1276-77 and again in 1282-83. As a consequence, Strata Florida was certainly remodelled in the early fourteenth century. Thereafter, the Black Death (1348-49) and the revolt of Owain Glyn Dwr (1400-09) took their toll. Despite late medieval revivals, by the early 1530s the suppression loomed large and by 1539, Strata Florida had closed. In 1887, the railway engineer, Stephen Williams, began to excavate Strata Florida and was placed in state care from the 1930s.
Source: Robinson, D.M. 2007. Strata Florida Abbey: CADW
M. Lloyd Davies, RCAHMW, 29 October 2008