Known in early times as ‘Domnach Bili’, meaning ‘church of the ancient or sacred tree’, the site later became known as Magh Bile, or Moville. According to tradition, St Patrick travelled here from Donagh and ordained Oengus, son of Ailill, though the historical accuracy of this founding story remains uncertain.

Today, visitors can explore the sub-rectangular graveyard containing the ruins of two medieval churches, a mortuary house or tomb shrine, and a tall ringed high cross standing guard at the western entrance. Of the South Church, only the southern wall survives; a 19m long rubble construction reaching 2.8m in height, with two window openings and the remnants of a wall press at its eastern end. The site served as an important religious centre throughout the medieval period, with one of its churches functioning as the parish church. Historical records from 1302 show the church valued at 40 shillings in ecclesiastical taxation documents, whilst various papal letters from the early 15th century detail a series of colourful disputes over the rectory, including accusations of perjury, notorious fornication, and the dilapidation of church funds for the benefit of concubines.

The annals provide glimpses of Cooly’s significance in medieval Irish society, recording the death of Aenghus, the airchinneach (erenagh) of Magh-bile in 953 AD, and the treacherous murder of Muircheartach, lord of Fordrum, within the church grounds in 1167. These events, alongside the numerous ecclesiastical appointments and disputes recorded in papal letters between 1412 and 1430, paint a picture of a religious site that remained politically and economically important well into the later medieval period. The modern town of Moville now lies just 1.2km to the east, whilst the ancient ruins continue to mark the spot where Christianity allegedly first took root in this corner of Inishowen.