Saint Marcan is an obscure figure in the catalogue of Irish holy men, and sites that carry a saint's name across both water and stone are relatively uncommon. The pairing suggests a landscape that was considered significant long before any fortification was built there, one in which the lough itself may have been regarded as sacred ground before the castle ever appeared on its shore.

The association with Saint Marcan connects this place to the early Christian period in Ireland, when local saints gave their names to wells, lakes, and small oratories scattered across the west of the country. Castles built beside or over such sites were often constructed by Gaelic lords or Anglo-Norman settlers in the medieval period, sometimes deliberately occupying ground that already carried religious or ceremonial weight. Without more detailed records, it is not possible to say who built the structure at St. Marcan's Lough, when it was raised, or what form it takes today. The name alone survives as the clearest evidence that something meaningful once stood at the water's edge.