Celso of Milan

Saint Celsus (Italian Celso), commonly called Celsus of Milan, is an early Christian martyr whose cult is inseparably linked with that of Saint Nazarius. He is commemorated with Nazarius on 28 July. Almost all biographical details derive from a late passio of little historical value; contemporary evidence is limited to the translation of relics carried out by Saint Ambrose of Milan in 395.

The passio presents Celsus as a young boy or adolescent whom Nazarius, a Roman Christian of mixed Jewish and Christian parentage, met during missionary journeys in Gaul. Nazarius is said to have instructed the youth and thereafter kept him as a companion. Together they are described as preaching in various cities of Gaul and northern Italy. Upon reaching Milan they were arrested, tried for their faith, and beheaded. Traditional dating places the martyrdom in the first century, often under Nero, but this chronology is anachronistic and cannot be verified. No reliable source records Celsus's place of birth, family, or exact year of death.

In 395 Bishop Ambrose announced the discovery of the bodies of Nazarius and Celsus. According to Paulinus the Deacon and later writers, the remains of Nazarius were found with blood still liquid; both bodies were treated as those of authentic martyrs. Ambrose translated Nazarius to the Basilica of the Apostles, which he had recently built on the road to Rome; the church later took the name San Nazaro in Brolo. Relics of Celsus were likewise honored in Milan, and a church dedicated to San Celso developed as a focus of his cult, eventually associated with a sanctuary of the Madonna.

The joint cult of Nazarius and Celsus became well established in Milan and spread through northern Italy. Medieval calendars and the Roman Martyrology retain the 28 July feast, describing Celsus as a boy who suffered with Nazarius. In art Celsus is typically shown as a youthful figure accompanying the older Nazarius, sometimes holding a palm of martyrdom. Because the documentary basis is so slender, modern historians treat Celsus as a saint whose existence is attested by a fourth-century Milanese cult rather than by a recoverable personal biography. No evidence indicates that he belonged to a religious order, held ecclesiastical office, or had a spouse or children; the hagiographical portrait is that of a youthful lay martyr.