Protasius (Italian: Protaso) was Archbishop of Milan. He is honored as a saint in the Catholic Church, with his feast day celebrated on 24 November, the day of his death.^[1]

Almost nothing is known about the life of Protasius. He was elected bishop of Milan in 328, and served until his death, about 343.^[2]

Athanasius of Alexandria, in his Apologia ad Constantium^[3], mentioned that Protasius was with him when he spoke to the Roman Emperor Constantius II; this episode can be dated about 342 or 343.^[4] In 343, Protasius attended the Council of Sardica and signed its decrees, standing up against the Arians and supporting the faith of the Council of Nicaea.^[2]

Protasius died about 343 on 24 November. His body was buried in Milan in the Church of San Vittore al Corpo (Saint Victor Maurus), where it is venerated still. A late tradition, with no historical basis, associates Protasius with a Milanese family, the Algisi.^[4]