It is not a font. It is a cross-base, the lower portion of what was once a standing stone cross, and the rectangular socket cut into its upper surface tells the real story: a mortise measuring roughly 27 by 13 centimetres and sunk 12 centimetres deep, shaped precisely to receive the tenon, or protruding foot, of a now-vanished shaft. The cross itself is long gone, but the base remains, a plain roughly worked piece of sandstone that tapers slightly from bottom to top and steps inward at its uppermost face.

The base sits just outside the east end of the nave of a medieval church, positioned along the church's southern wall, which is itself a significant placement in early Irish ecclesiastical tradition, where the east end was liturgically the most important. The broader site at Tullaherin is unusually dense with early medieval material. Alongside the church and cross-base, the graveyard contains a round tower, the kind of tall tapering stone structure built from roughly the ninth century onward and associated with monastic settlements, as well as two ogham stones, upright or re-used stones inscribed with ogham, an early medieval script that uses a series of notches and lines along a central stemline to render names and words in an early form of Irish. The combination of round tower, ogham stones, medieval church, and cross-base in one small graveyard points to a site with a long, layered history of religious use, even if much of the detail has not survived.