William Jenkins Rees, in his book Lives of the Cambro British Saints, describes Tathan as the only son of the Irish King Tathetus.
In preference to succeeding his father as king, Tathan followed the advice of an angel and sailed from Ireland to Britain, taking eight disciples with him.
His boat sailed up the River Severn and landed in the medieval Kingdom of Gwent.
[3] Tathan was feted by King Caradoc and founded a monastic school at Venta Silurum (Caerwent).
King Gwynllyw of Gwynllwg sent his seven-year-old son, Cadoc to study under Tathan.