This Monastery was probably founded in the late 5th or early 6th Century by St Ciaran of Saighir. It was attacked by Viking raiders in 861 but they were repelled by Cerbhall of Ossory. In 1156 the monastery was attacked again and burned, the elegant Round Tower - the bell tower - is all that remains of the early monastery. At 8 stories high, with each level reached by a wooden ladder it was amongst the tallest in Ireland.
In the 16th century a Priory of Augustine Cannons Regular - priests who lived in the community - was founded here under the patronage of the Anglo Normans. The present ruined church might have been part of the Augustine Priory. It has been heavily altered since the 13th century. A small chapel beside the church contains the tomb of John Mac Gillapatrick, carved around 1540 by Rory O Tunney. In the 19th century the west doorway and east window were taken down and moved to Johnstown Church of Ireland while a baptismal font and a representation of the Crucfixion were moved to the Catholic Church there.