St Ismaels 4 is a rough, cross-carved slab with rounded top. In 2007 it was located at the National Museum of Cardiff (NPRN 167), prior to display in St Ishmael's Church, St Ishamel's (NPRN 414087). The stone was found in 2003 during the excavation of eight burials (one a child), three in long cist graves, on the cliff-edge at Great Castle Head, Longoar Bay. One of the adult burials yielded a 7th century radiocarbon date. The stone was face-down and forming one of the lintel stones over an adult grave. It is thought to have originally been an upright grave marker, reused shortly afterwards.

The stone is broken diagonally across the bottom. Dimensions are given as 59cm height x28cm width x 5cm diameter. It is carved on one of its broad faces with a deeply incised, linear, roughly equal-arm cross. It is thought to be 7th- to 9th-century in date.

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

N Vousden, 6 November 2018