This is a cross base, the part of a standing cross that was set into the ground to keep the upright shaft stable, and in this case the shaft it once held has long since disappeared, leaving only its socket as evidence that something significant once stood here.

The stone was documented by Patrick Healy in a 1972 survey of ancient monuments at Glendalough, at which point he recorded it as a slab of mica schist measuring 1.17 metres long, 0.45 metres wide, and just 0.12 metres thick. Running through it is a rectangular mortise, a cut-through socket measuring 0.32 metres by 0.14 metres, into which the base of a cross shaft would have been fitted. Mica schist is a locally available metamorphic rock with a characteristic layered, slightly glittering surface, and its use here suggests the base was fashioned from material close to hand rather than imported stone. The base sits approximately 12.3 metres to the south-east of the south-east corner of the cathedral chancel, placing it within the broader monastic enclosure of Glendalough, the early medieval site associated with Saint Kevin and known in Irish as Gleann Dá Loch, the valley of the two lakes.