St Tathan (Tathyw), was perhaps an Irish monk, also a royal, who sailed up the Severn for a place for a hermitage. He founded a monastery in the old Roman ruins of Caerwent at Llantathan in the Vale of Glamorgan. He was known for his learning and called the ‘Father of all Gwent’. St Cadoc and St Malo (6C) trained under him.
A burial was found in 1910 and re-buried in the church; it was believed to be that of St Tathan but this is not at all clear. In 1906 a pewter bowl with a faint Chi-Rho monogram scratched on it was also found. This is dated to about 375 and is the first direct proof that Christianity had arrived in Wales. It is now in Newport museum.