John 6:19

ἐληλακότες οὖν ὡς σταδίους εἰκοσιπέντε ἢ τριάκοντα. The Vulgate renders “cum remigassent ergo,” and modern Greek ἐκωπηλάτησαν, rightly; see Aristoph., Frogs, 195; and other passages in Elsner. The stadium was about 194 (Rich gives 202) yards, so that nine rather than eight would go to a mile. The disciples had rowed about three miles. [The best discussion of the direction they were taking is in the Rob Roy on the Jordan, p. 374.] θεωροῦσι τὸν Ἰησοῦν περιπατοῦντα ἐπὶ τῆς θαλάσσης “they see Jesus walking on the sea”. It has been suggested that this may only mean that Jesus was walking “by” the sea, ἐπί being used in this sense in John 21:1. But that ἐπί can mean “on” the sea is of course not questioned (see Lucian's Vera Historia, where this incident is burlesqued; also Job 9:8, where, to signalise the power of God, He is spoken of as ὁ περιπατῶν ὡς ἐπʼ ἐδάφους ἐπὶ θαλάσσης). Besides, why should the disciples have been afraid had they merely seen Jesus walking on the shore? They manifested their fear in some way, and He says to them, Ἐγώ εἰμι, I am He, or It is I.