Towards the end of the Peloponnesian War (if we may suppose that Polyaenus, writing in the second century A.D., was not guilty of anachronism) the purple cloak signal (φοινικὶς [Greek: phoinikis]) comes into evidence. Conon, the Athenian commander, was in the year 406 B.C. off Mitylene, flying before Callicratidas the Spartan, who had twice as many ships. Observing that the Lacedaemonian ships had, in the ardour of pursuit, broken their ranks, Conon raised the "Phoinikis," which was the signal he had pre-arranged with the commanders of his ships, and, turning together, the Athenian ships bore down on their pursuers, then in disorder[342].
The Rhodians, in the second century B.C., made signals in the early manner by raising the "signum" or military ensign. Livy relates that Eudamus, when hard pressed in his action against the Syrian fleet under Hannibal (191 B.C.) made use of such a signal to call his unengaged ships to the rescue[343].
The earliest code of naval signals is that drawn up in the ninth century A.D. by the Emperor Leo VI in his treatise on Tactics[344]. Leo in the Introduction to his nineteenth chapter explains that he has been unable to find anything on this subject among ancient Greek writers except a few scattered references and that his knowledge is mainly derived from the experience of his Generals.
In this nineteenth chapter, which deals with Naval Warfare (Περὶ ναυμαχίας [Greek: Peri naumachias]) he says:
39. Let there be some standard (σημεῖον [Greek: sêmeion]) in your ship, either a banner (βάνδον [Greek: bandon]) or a streamer (φλάμουλον [Greek: phlamoulon]) or something else in some conspicuous position, to the end that you may be able, thereby, to make known what requires to be done, and that the rest may set themselves to carry out the course of action decided on, whether it be to fight or to withdraw from fighting; to open out to surround the enemy, or to concentrate to the relief of an endangered portion of the fleet; to slow the rowing or increase speed; to make an ambush, or, emerging from ambush to attack the enemy; or, in general, whatever the signal that has its origin in your ship, that the others, by keeping an eye on her, may be able to execute it.