Firmilian (Greek: Φιρμιλιανός, Latin: Firmilianus, died c. 269 AD), Bishop of Caesarea Mazaca from c. 232, was a disciple of Origen.
He took an active part in the mid-3rd century controversies over rebaptising heretics and readmitting lapsed Christians after the persecutions of Decius and was excommunicated by Pope Stephen I for his position.
"To his contemporaries his forty years of influential episcopate, his friendship with Origen and Dionysius, the appeal to him of Cyprian, and his censure of Stephanus might well make him seem the most conspicuous figure of his time" (Wace).
At the end of the summer of 256, he sent the deacon Rogatian to Firmilian with a letter, together with the documents on the subject—letters of the pope, of his own, and of his council at Carthage in the spring, and the treatise De Ecclesia Catholica Unitate.
In a letter to Pope Sixtus II (257–58), Dionysius mentions that in the controversy over rebaptism of the lapsed, Pope Stephen had refused communication with Helenus of Tarsus, Firmilian, and all Cilicia and Cappadocia, and the neighbouring lands (Eusebius, VII, v, 3–4), a subject touched on in the sole surviving letter of Firmilian, a response to Cyprian.
[6] This was the practice even of the African Church till Agrippinus, bishop of Carthage, in the close of the second century, changed it, fifty years before St. Cyprian.
The threat of excommunication only served to incense Firmilian who considered it "ridiculous" that Stephen demanded nothing but the use of the Trinitarian formula.
Moreover, he disagreed that Rome preserved the Apostolic traditions unchanged, for it differed from Jerusalem as to the observances at Easter and he disputed Stephen's authority to excommunicate them.
"I am justly indignant with Stephen's obvious and manifest silliness, that he so boasts of his position, and claims that he is the successor of St. Peter on whom were laid the foundations of the Church... You have cut yourself off—do not mistake—since he is the true schismatic who makes himself an apostate from the communion of ecclesiastical unity.
His great successor in Cappadocia, St Basil of Caesarea, mentions his view on heretical baptism without accepting it (Epistle clxxxviii), and says, when speaking of the expression "with the Holy Ghost" in the Doxology: "That our own Firmilian held this faith is testified by the lógoi which he has left" (De Spiritu Sancto, xxix, 74).