Saturninus was a popular name in the late antique Roman empire, so there are several obscure saints who all bear that name. At least two potential candidates are the saints with the name Saturninus who we honor today, and both were martyred in the first centuries of the Church. Relics of St. Saturninus rest in the reliquary chapel in the Basilica, but it is unclear which Saturninus the relics belong to.
The legend of Saints Perpetua and Felicity tells of a priest, Saturninus, who was one of their companions and ministered to them during their time in prison, comforting them as they prepared for martyrdom and he anticipated his own. This may or may not be the same Saturninus as Saturninus of Rome.

Saturninus of Rome was a priest who ministered with Sisinius, a deacon. They were imprisoned during a period of persecution of Christians, potentially during the reign of Septimius Severus and forced into manual labor before being tortured and killed, most likely around the year 203 AD.

Saturninus of Toulouse was the first bishop of the city of Toulouse in France, and was known to have converted many with his preaching and by working miracles. One of the popular cults in the late Roman empire was the cult of Mithras. The cult of Mithras was a popular “mystery religion,” which featured secret initiation rites and cultic sacrifice. A temple to Mithras had long stood at the heart of Toulouse but Saturninus’ presence and preaching offended the priests there. They seized him and told him to offer sacrifice to Mithras or face death. Saturninus chose death, saying, “I worship only one God, and I am ready to offer a sacrifice of praise.” They tied him to a bull that was to be sacrificed at the temple and then prodded the animal to run through the streets until Saturninus was dead. Saturninus was thought to have been martyred around the year 257 AD.

Churches were built over the bodies of both of these saints in their respective cities. An image of St. Saturninus of Toulouse is used here with permission from Catholic.org.

St. Saturninus, who showed great dedication to God, even under the threat of death—pray for us!