The oldest part of the church is to the south, with the north aisle added later – and is an especially good example of nave-arcading with four handsome pointed stone arches of the Doric Order.

The old church was used as the burial place for the Ulster-Scots Montgomery’s in the 17th Century, whose graves would have been marked with large flat stones recording names. There are two vaults at the Priory for the Colville family and the Stewart family (successors to the Montgomery’s as landlords), with a large tomb for Frederick Stewart, 4th Marquis of Londonderry.

Last used for public worship in 1817 when the new St Mark’s Parish Church was opened, the church served as a courthouse in its latter days.  Its walls are carefully preserved and enclose gothic archways, pillars, enormous tombs and memorials.  

One reliable mid-19th century source reported that a former minister of the Priory returned one night with a horse and cart and dug up a lot of bones of the people who were buried here, taking them to his farm at Moneyreagh and using them as fertiliser on his potatoes...