Manus O' Donnell, son of the chieftain of Tyrconnail, summoned the help of the minor Donegal clans of O'Boyle, Mac Sweeney and O' Gallagher, and the combined O' Donnell forces, having marched from Donegal town through Barnesmore Gap. They pitched their camp at Drumleen, where they were joined by a contingent of the finest of the O'Doherty warriors from Inishowen.
The O'Neill clan were encamped at Knockavoe, overlooking the river valley, awaiting some of their allies from Connaught and Leinster.
In the early hours of 15th June 1522 the O'Donnells made a surprise two pronged attack across the Foyle on the O'Neill camp with complete success. Following a savage encounter which lasted throughout the long summer day ranging from the Greenbraes of the Foyle to Lough Moneen (the old name for Murlog), the outcome according to the annals, was that the O'Neills were defeated with the loss of nine hundred men and many of their best leaders and great quantities of armour, provisions and strong liqueurs were seized by the victors.
Many of those who perished in the battle were buried with christian rites in mass graves on the hillside (now church street) below the friary. Early in the twentieth century, long buried remains were unearthed during pipe laying operations in the Church Street/Patrick Street area.
In 1523 the O'Donnells again invaded Tyrone and burned many buildings including the friary in Strabane. The settlement was confiscated by the crown in 1609 and the lands were granted to Robert Leicester.
In 1524 and 1525 strife continued between the local clans and in consequence Manus O'Donnell, now the O'Donnell chieftain, erected a castle in Lifford (near the courthouse) which brought calm in the area for the next thirty years.
In 1532 Manus, now residing at the castle embarked on a project completely different. He compiled all existing documents and poems, in Latin and in Irish relating to Colmcille. The work, bound in a large cellum folder is preserved in the Bodleian Library at Oxford.
Note: This text has been sourced from The Fair River Valley: Strabane though the Ages by Jim Bradley.