The slab is a recumbent tapering gravestone of the late medieval period, measuring just under 1.8 metres in length, its edges carefully bevelled, its upper face carved with a cross in outline at either end, the two crosses joined by connecting shafts. It is the kind of object that is easy to step around without a second thought, yet the belief attached to it, that St. Sylvester himself lies beneath, gives the stone a quiet weight that outlasts its modest dimensions.

The slab is one of two late medieval examples at Donard church, and together they offer a small study in the variation possible within a single tradition. The second stone, shorter and thicker, carries similar ornament but executed with noticeably less refinement, a cruder hand working the same basic vocabulary of cross and shaft. Where the first slab lies horizontal inside the church, close to where worshippers would have entered, the second now stands upright against the outside of the eastern gable, repositioned at some point from its original resting place. Christiaan Corlett, writing in 2003, documented both stones as part of the archaeological record of the site.