Begerin, roughly 450 metres long and no more than 200 metres wide at its broadest, sat in the shallow water of the harbour's northern reach. The land drainage and reclamation works of that period absorbed it into the mainland, but the oval raised graveyard at its north-eastern angle, defined by old field banks and measuring around 83 metres across, still marks where one of Ireland's earlier monastic foundations once stood. An early medieval church founded on a disappearing island, and now marooned instead in flat agricultural land, has a quietly disorienting quality.

The monastery was established in the fifth century by Bishop Ibar, sometimes written as Iobhar, who was probably born somewhere in the Louth or Meath area and is thought to have died around 504 to 510. His feast day fell on the 23rd of April. Ibar may have had connections with other early Irish saints, including St. Abán of nearby Adamstown. The monastery survived long enough to be plundered by Vikings in 819, an event recorded alongside a simultaneous raid on Ardcavan, a neighbouring site on the harbour. Despite that violence, the community continued: the death of an abbot named Crunnmhael is recorded in 964. A wooden statue of the saint kept at the church drew pilgrims as late as the 1680s, suggesting some form of devotional life persisted on the island well into the early modern period. What remains of the nave and chancel church stands to roughly three metres in places, though the chancel itself is almost entirely gone, and a single undecorated window opening survives in the south wall of the nave. A granite slab incised with a cross within a rectangle sits towards the eastern edge of the graveyard.

Two carved schist stones that were once at the site are now held elsewhere. One, with a ringed cross decorated in elaborate interlace on one face, is in the National Museum of Ireland; scholars have attributed Viking influence and a tenth-century date to it. The other, slightly taller and with a damaged circular head, is in the Wexford County Museum in Enniscorthy. Its carvings include a cross in relief, two figurative panels, and a single horseman, and a ninth-century date has been suggested, with a possible Cornish influence noted. Both stones are cross-slabs, a form of early medieval carved monument common across Ireland and Britain, typically erected as grave markers or devotional objects. Their dispersal is a reminder of how thoroughly the island's material culture has been scattered, even if the ground itself, raised and banked, still holds its ancient shape.