Passage 6.20.13
πρῶται μὲν δὴ ἑκατέρωθεν αἱ πρὸς τῇ στοᾷ τῇ Ἀγνάπτου χαλῶσιν ὕσπληγες, καὶ οἱ κατὰ ταύτας ἑστηκότες ἐκθέουσιν ἵπποι πρῶτοι· θέοντές τε δὴ γίνονται κατὰ τοὺς εἰληχότας ἑστάναι τὴν δευτέραν τάξιν, καὶ τηνικαῦτα χαλῶσιν αἱ ὕσπληγες αἱ ἐν τῇ δευτέρᾳ τάξει· διὰ πάντων τε κατὰ τὸν αὐτὸν λόγον συμβαίνει τῶν ἵππων, ἔστʼ ἂν ἐξισωθῶσιν ἀλλήλοις κατὰ τῆς πρῴρας τὸ ἔμβολον· τὸ ἀπὸ τούτου δὲ ἤδη καθέστηκεν ἐπίδειξις ἐπιστήμης τε ἡνιόχων καὶ ἵππων ὠκύτητος.
First at each side near the Stoa of Agnaptos the starting-gates are lowered, and the horses standing at these gates are the first to rush out. As they rush forward, they come level with those arranged by lot to hold the second position, and at that moment, the gates of the second rank are opened. Likewise, the same procedure occurs through all the horses in order, until they form a straight alignment with each other at the prow-shaped turning-post. After this point, the contest is established as a display of the skill of the charioteers and the swiftness of their horses.