Cilgerran 1 stands in the churchyard of St Llawddog's Church (NPRN 402530). It was first recorded in 1698/1699 when the entire inscription was visible.
The stone is a rough, unshaped square-section pillar of spotted dolerite, which tapers towards the top. Measurements are given as 244cm height x 38 > 30.5cm x 40.5 > 30.5cm. The lower part is buried covering part of its inscriptions. The roman-letter, Latin inscription is incised in two lines running vertically downwards. It has been translated as `of Trenegussus son of Marcus-Treni, here he lies?. The ogam inscription runs vertically up the stone. It has been translated as `of Trenagus[.] son of Macus-Treni?. The inscription is thought to date to the second half of the 6th century. A lightly-scratched carved cross is of uncertain date, probably later.

Sources include:
Edwards, N. 2007, Corpus of Early Medieval Inscribed Stones and Stone Sculpture in Wales

N Vousden, 20 November 2017