sentences:  Fergus, having his principal seat on Palace Isle, Loch Fergus, erected the ‘Prioratus Sanctae Mariae de Trayl’ (St. Mary's Isle Priory) in penitence for rebellion against King David I of Scotland.Whether or not the endowment was made for this purpose, Holyrood Abbey established a daughter house there which is on record by the time of a grant by Lochlann, Lord of Galloway sometime between 1189 and 1193.A "prior of Galloway" by the name of "William" appeared alongside the Abbot of Holywood and his prior in a document preserved by St Andrews Cathedral Priory dated to 1173, and so it is possible that this William is the earliest recorded Prior of St Mary's Isle.