This roughly shaped decorated stone (with three linked pairs of knots on one face and a diagonally set pattern of square frets on the other), was first recorded in the churchyard in 1808. It was moved into the church in 1960 and currently sits propped against the interior south wall. Both patterns occur on a stone found in West Lothian (Abercorn). The knotwork is virtually identical to knotwork on Llanfihangel Ystrad 2, thought to have originated at Maes Mynach, Cribyn (NPRN 303883)- slightly east of medieval Capel Sant Silin (subsequently removed to St Hilary's Church, Llanilar (NPRN 400464). Silian 2 is thought to be ninth/tenth century in date. Both patterns are similar to that on Llanddewi Aber-arth 1 at St David's Church, Llanddewi Aberarth (NPRN 419559), thought to be ninth to tenth century in date. In May 2013 another ninth/tenth century carved stone, Silian 3 (NPRN 419114) was rediscovered in the Nant Tawelan, some 40m south St Sulien's Church (NPRN 402554). Silian 1 (NPRN 419117), a fifth/sixth century inscribed stone, with eighth/ninth century incised cross, is built into the church's exterior south wall.

The rectangular pillar-stone measures some 1m length x 30cm width x 15cm diameter. The main faces bear vertical panels of carved ornament in low relief, with eight-cord plain knotwork at the front and a square fret-pattern, disposed diagonally, at the back.

Sources include:
Edwards, N, 2007, A Corpus of Early Medieval inscribed stones and Stone Sculpture in Wales
Nash-Williams, V.E., Early Christian Monuments in Wales

N Vousden, RCAHMW, 1 July 2013