The dashed line traces a rough circle of roughly sixty metres in diameter around a small hill overlooking the valley of the Castlebar River in County Mayo. It follows the lower contours of the hill rather than cutting across the landscape arbitrarily, and at the summit sit a round tower and the remains of a church. The arrangement is neat enough to make a person wonder whether the cartographers were recording something much older than their own century.

Early ecclesiastical enclosures were a common feature of monastic settlements in early medieval Ireland, typically defined by a circular or oval boundary, sometimes a bank and ditch, that separated the sacred inner ground from the secular world beyond. The way the dashed line at Turlough hugs the natural topography of the hill, with a round tower and church occupying the high point inside it, fits that pattern well. Round towers, which served variously as bell towers, places of refuge, and symbols of ecclesiastical prestige, were almost always built within established monastic precincts. The spatial logic here is suggestive. The difficulty is that nothing at ground level currently confirms the enclosure as a physical reality. No earthwork, bank, or ditch has been identified to match what the old map implies, leaving the question of whether the 1838 surveyors were recording a visible feature, following a local tradition, or simply tracing the natural edge of the hill, genuinely open.