The Congregation of the Sisters of Christian Instruction, the Sisters’ formal title, was founded in 1820 and later came into possession of the grounds of the ruined Benedictine Abbey of St. Gïldas in the Woods; hence their popular name, Sisters of St. Gildas.
St.Gildas, patron saint of Vannes, was one of those dear Celtic saints who roamed all over the place. Son of a British chieftain, he studied under St. Illtyd in Merthyr Vale. He left Wales for Ireland and from Ireland went to preach the Gospel in the north of England. At the early age of 34 he packed it in and sailed to retirement in Brittany. His hermitage on the Isle of Houat was invaded by the curious who forced him to start a religious colony on the mainland. In his 44th year he wrote of the early phases of the Anglo-Saxon conquest of Britain which remains the only contemporary British version of the events of 450 – 550. He died in 570.
(Taken from a history of the parish written, we think, in the late 1960s)
Note that there are 2 biographies of the saint, written some centuries after his death, one by a breton monk and the other by a Welshman. The differences between them have led various commentators to argue that there were actually 2 Gildas, one British and one French. However, the Catholic Encyclopedia entry sides with a number of other writers who believe there was in fact only one St Gildas.