Xen. Ana. 4.7.21-25
And on the fifth day they were arriving [present-tense] on the mountain. Theches was the name of the mountain. And after the first troops came to be upon the mountain and they saw the sea, a great cry went up. Xenophon heard it and the rearguard thought that other enemies were attacking in the front, for they were followed from behind out of the burned countryside. And the rearguard had set up an ambush and had both killed and captured some of these, and took about twenty rawhide shields made from shaggy skins. But then more people and closer took up the cry and constantly the ones going up took up running at top speed after those continuing to cry and the cry became much [πολλῷ - or does he mean more people?] louder with so many more people having come. And to Xenophon it seemed that something major was happening, and he mounted his horse and after gathering Lukius and his horses, went to help. And quickly they heard the soldiers crying "the sea the sea" and crowding in. And then the entire rearguard took up the run, and the pack animals and the horse were driven on. And after all had come up on the top, they were hugging each other and the generals and the captains were crying. And appearing from somewhere nearby the soldiers were carrying [present-tense] rocks and they set up a huge column.καὶ ἀφικνοῦνται ἐπὶ τὸ ὄρος τῇ πέμπτῃ ἡμέρᾳ· ὄνομα δὲ τῷ ὄρει ἦν Θήχης. ἐπεὶ δὲ οἱ πρῶτοι ἐγένοντο ἐπὶ τοῦ ὄρους καὶ κατεῖδον τὴν θάλατταν, κραυγὴ πολλὴ ἐγένετο. ἀκούσας δὲ ὁ Ξενοφῶν καὶ οἱ ὀπισθοφύλακες ᾠήθησαν ἔμπροσθεν ἄλλους ἐπιτίθεσθαι πολεμίους· εἵποντο γὰρ ὄπισθεν ἐκ τῆς καιομένης χώρας, καὶ αὐτῶν οἱ ὀπισθοφύλακες ἀπέκτεινάν τέ τινας καὶ ἐζώγρησαν ἐνέδραν ποιησάμενοι, καὶ γέρρα ἔλαβον δασειῶν βοῶν ὠμοβόεια ἀμφὶ τὰ εἴκοσιν. ἐπειδὴ δὲ βοὴ πλείων τε ἐγίγνετο καὶ ἐγγύτερον καὶ οἱ ἀεὶ ἐπιόντες ἔθεον δρόμῳ ἐπὶ τοὺς ἀεὶ βοῶντας καὶ πολλῷ μείζων ἐγίγνετο ἡ βοὴ ὅσῳ δὴ πλείους ἐγίγνοντο, ἐδόκει δὴ μεῖζόν τι εἶναι τῷ Ξενοφῶντι, καὶ ἀναβὰς ἐφ’ ἵππον καὶ Λύκιον καὶ τοὺς ἱππέας ἀναλαβὼν παρεβοήθει· καὶ τάχα δὴ ἀκούουσι βοώντων τῶν στρατιωτῶν Θάλαττα θάλαττα καὶ παρεγγυώντων. ἔνθα δὴ ἔθεον πάντες καὶ οἱ ὀπισθοφύλακες, καὶ τὰ ὑποζύγια ἠλαύνετο καὶ οἱ ἵπποι. ἐπεὶ δὲ ἀφίκοντο πάντες ἐπὶ τὸ ἄκρον, ἐνταῦθα δὴ περιέβαλλον ἀλλήλους καὶ στρατηγοὺς καὶ λοχαγοὺς δακρύοντες. καὶ ἐξαπίνης ὅτου δὴ παρεγγυήσαντος οἱ στρατιῶται φέρουσι λίθους καὶ ποιοῦσι κολωνὸν μέγαν.
ἐπὶ for accusative v. genitive. The difference really seems to be motion v. rest here.
ἐπιτίθημι - verified that the middle was the sense "attack" and that ἐπιτίθεσθαι wasn't passive
ἐνέδρα - ambush (I should have known this one)