For trine immersion an early authority is Tertullian, c. Praxeam xxvi. cf. Greg. Nyss., De Bapt. ὕδατι ἑαυτοὺς ἐγκρύπτομεν …καὶ τρίτον τοῦτο ποιήσαντες. Dict. Ch. Ant. i. 161.