Prior to Christianity becoming the official religion of the Roman Empire, Christians in Britain were persecuted by Romans. Alban sheltered Amphibalus in his home, and was converted to Christianity by him. When Roman soldiers came in search of the priest, Alban and Amphibalus exchanged cloaks, and Alban was arrested instead of Amphibalus. Alban was executed on the current site of St Albans Cathedral.
It is unlikely that Amphibalus was the genuine name of the priest - it is likely to be Geoffrey of Monmouth's misunderstanding of the Latin word used for the cloak, amphibalus, passed to Alban. Similarly, other details concerning the life of Amphibalus should be approached with historical caution. He is believed to have come from Caerleon, and to have converted numerous Britons to Christianity, including Saint Stephanus and Saint Socrates with whom he fled to Wales. He was later caught by the Romans, and returned to Verulamium where he was executed.
Remains identified as of Amphibalus were discovered at Redbourn in Hertfordshire, England, near the town of St Albans, in 1178, and placed in the Abbey Church. The first shrine to Saint Amphibalus was destroyed when the roof of the abbey collapsed. A new shrine was built circa 1350, but was destroyed during the Dissolution of the Monasteries, and the remains of Saint Amphibalus were dispersed. Fragments of the shrine were found in the nineteenth century and can be found in St Albans Cathedral.