During his episcopate, the remains of St. Ferreolus were discovered, and were translated by Mamertus to a church in Vienne, built in honour of that martyr. St. Mamertus was the founder of the Rogation Processions, according to Sidonius Apollinaris, and his second successor, Avitus In connexion with these intercessory processions, Mamertus summoned a synod at Vienne between 471 and 475. About 475 he attended a synod at Arles, which dealt with the predestination teaching of Lucidus, a Gallic priest. As this is the latest information we possess concerning him, we may assume that he died shortly afterwards.