Strabane (strəˈbæn; ) is a town in County Tyrone, Northern Ireland. Strabane had a population of 13,172 at the 2011 Census. It lies on the east bank of the River Foyle. It is roughly midway from Omagh, Derry and Letterkenny. The River Foyle marks the border between Northern Ireland and the Republic of Ireland. On the other side of the river (across Lifford Bridge) is the smaller town of Lifford, which is the county town of Donegal. The River Mourne flows through the centre of the town and meets the Finn to form the Foyle River. A large hill named Knockavoe, which marks the beginning of the Sperrin Mountains, forms the backdrop to the town. The locale was home to a group of northern Celts known as the Orighella as far back as the fourth century when the territories of Owen (later Tír Eoghain) and Connail (later Tír Chonaill - mostly modern County Donegal) were established, and Orighella were assimilated into the Cenél Conaill. With the arrival of Saint Patrick, a mission established a church in the area near Castlefin, and having visited the Grianán Aileach for the conversion of Owen, returned along the Foyle river, establishing a further church at Leckpatrick (the name means 'the flagstone of St. Patrick'). A later church was established at Lifford/Clonleigh by a mission headed by St. Colmcille. In AD 586 St. Colgan established a monastery at Camus [from whence the parish of Camus-Juxta-Mourne gets its name]. Other monasteries and religious sites were established at this time at Urney, Ballycolman, Donagheady, and Artigarvan. Vikings arrived at Lifford in AD 832 and maintained a presence on the Foyle until AD 863 when they were expelled by Áed Findliath. The regional seat of power was to be the Grianán Aileach until 1101, when it was destroyed by the O'Briens of Thomond, and was then moved to Urney, three miles outside Strabane. In 1243, the seat of power for all Tyrone and the O'Neill dynasty was moved to Cookstown. It was during this epoch, in AD 1231, that Franciscan friars established a religious foundation on what is now the old graveyard at St.