A castle once occupied its centre, known in the historical record as 'Baile Bhaiter', but the island itself appears to be considerably older than any medieval stonework. The lough has shrunk considerably due to drainage over the centuries, which makes the island's origins harder to read at a glance, yet the layering of human use written into its topography is quietly remarkable.

When the site was examined in 1981, it was identified as a possible crannog, the term for an artificial or artificially enlarged island, typically built during the early medieval period in Ireland as a defended dwelling place. The island has a natural core, which would have provided a stable base for such construction, but the edges show signs of deliberate land accumulation, material added outward to extend the usable surface, and this work is thought to pre-date the later castle. It is a pattern seen elsewhere: a prehistoric or early medieval island settlement that a later medieval builder recognised as a convenient and defensible platform, and simply built on top of. The parallel sites most commonly cited are Clogh Oughter in County Cavan, where an Anglo-Norman tower house rises from a crannog in Lough Oughter, and Island McHugh in County Tyrone. An iron arrowhead registered in the National Museum of Ireland's finds index, recorded under registration number 1934: 488, may be associated with the site, though the exact circumstances of its discovery are not documented in detail.