sentences:  The O'Caithnaidhs, who were chiefs of Erris before the Norman Invasion in the 12th century AD, had their stronghold in Glencastle.They were defeated by the O'Connors who then took over the fort until 1303 when it was conquered by the Barrett Normans.In 1540 the Barrett's castle in Glencastle was so well known that the English called Erris, 'Arrus Dundohmnaill'.