Mathry 1 stands in the porch of Church of the Holy Martyrs, Mathry (NPRN 412501). It was first noted around 1698 when it was standing in the churchyard, and its inscription was recorded. In 1937 it was rediscovered upside-down and in use as a gatepost in the west entrance to the churchyard. It was moved to its current position before 1950.

The stone is a rough, rectangular slab of microgranite, carved on both broad faces (A and C). Dimensions are given as 135cm height x 99cm width x 18 .9cm diameter. The stone has three gate-hanger holes in the top of face A, two of which go right through the stone. The top of the stone is now missing, meaning most of the top line of the inscription on face A, recorded in 1698 has now been lost. The roman-letter, Latin inscription has been translated as `Maccudiccl son (of) Caticus?, Towards the top of the left angle of faces B and C is a fragmentary incised ogam inscription, translated as `MAQ[.D]? Both inscriptions are thought to date to the 6th century. Towards the top of face C is a lightly incised circle (now incomplete), formed of double-line moulding in low relief. The carving is thought to be 8th century or later.

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

N Vousden, 11 October 2018