A hilltop in County Kildare that several roads converge upon, as if drawn there by some older logic, turns out to have been doing exactly that for well over a thousand years. The site at Oldkilcullen sits at around 150 metres above sea level on a moderately steep-sided hill, and the name itself encodes its character: Kilcullen derives from the Irish Cill Chuilinn, meaning 'church of the steep slope'. That the place was once important enough to attract Viking raiders, sustain a succession of abbots and bishops across several centuries, and eventually produce a cluster of high crosses and a round tower suggests a community of considerable standing, even if the landscape now holds its history quietly.

The foundation is traditionally associated with two early figures: Isernius, who died in 468, and MacTail, who died in 548. Isernius is thought to have been a companion of Patrick, which would place the origins of this community among the earliest generations of Christianity in Ireland. By the later eighth century, the deaths of abbots were being recorded, and bishops appear in the annals during the tenth and eleventh centuries. Those same centuries brought violence: the monastery was plundered by Amhlaibh and the Norse of Dublin in 937 to 938, and raided again in 944. A stone church is mentioned in 1037, which was a significant marker of permanence and investment for its time, and the monastery was burned in 1114. Little of the early monastic fabric has survived, though some curving field boundaries on the hill may preserve the outline of the original monastic enclosure, the roughly circular boundary that typically defined an early Irish monastery. What does survive above ground speaks to the site's later flourishing: three high crosses, the stump of a round tower, and the ruins of a church. High crosses were carved monuments, often elaborately decorated, that served as focal points for prayer, preaching, and the marking of sacred space; their presence here in multiples points to a community with both resources and ambition.