Castorius is the name of several early Christians:
1. The brother of the constable Nicostratus, converted and martyred with him (see Tillemont, Memoires, 4:521, 528). His feast is marked July 7, but Tillemont observes that they could not have suffered before the 17th. Claudius, the jailer, and his sons, Felix and Felicissimus, were also converted and martyred along with them, A.D. 286.
2. A martyr at Nicomedia, commemorated March 16.
3. A martyr at Tarsus, commemorated March 28.
4. The name of three Roman presbyters in, A.D. 303, one condemned, with Marcellinus, for apostasy, aid also for betraying the granaries of the Church, the other two accusing him (Labbe, Concil. 1, 939-943).
5. The brother of Maximian (q.v.). We meet with him in the year 402 (Tillemont, 13, 388; Labbe, Concil. 2, 1101). The brothers were Donatists, and became Catholics. Maximian was appointed to the see of Vagina, but a scandal was raised against him, and he withdrew. Castorius was urged to take his brother's place by Augustine and Alypius (Epist. 69, vol. 2, p. 230), whom Tillemont (Memoires, 13, 991) supposes to have been then at Vagina, where Castorius had been elected, and whence he retired.
6. The notary and representative or unto of pope Gregory I at Ravenna, against whom the people of that town laid complaints (Gregory, Epist. 6, 31).
7. Bishop of Rimini, ordained reluctantly by Gregory I, at the request of the people, but resigned because of infirmity (Gregory, Epist. 2, 35).
8. A deacon, charged with examining into the life of the bishop of Pesaro and his presbyters (Gregory, Epist. 8:19).