The few scattered references to signals found in early Greek literature are so vague in their terms that they leave us in doubt whether the ancient Greeks or their predecessors on the waters of the Eastern Mediterranean made any use of flags for signalling purposes. It seems probable that the earliest signals were given by raising the naval standard which, as we have seen, found a place at the stern of the Phoenician ships of war at least as early as 400 b.c., and that the Greeks adopted this method from the Phoenicians, substituting a cruciform standard for the Phoenician Crescent and Globe.
When Thucydides tells us that the "semeion" was raised in the Greek fleet we may, in default of some better explanation, assume that the officer in command seized the cruciform standard and elevated it at arms' length. Such a signal might be rendered more conspicuous by throwing a military cloak of bright colour over the arms of the cross before raising it and, as already remarked, it seems highly probable that the sign known as Phoinikis (φοινικὶς) originated in this manner.
The earliest recorded instance of a signal at sea is probably that mentioned by Herodotus[338] as having been made by Xerxes in the year 480 b.c., when on quitting Therma in his expedition to Greece he embarked in a Sidonian ship and "gave the signal (σημήιον) to the rest of the fleet to get under way." A more characteristic—or more frequently mentioned—use of the "semeion" was as a signal to commence action. The fleet fitted out by the Corinthians against the Corcyreans in the year 433 b.c. met with a joint fleet of Corcyrean and Athenian ships. Both the opposing fleets drew up in rank and the "semeia" were then raised on both sides (τὰ σημεῖα ἑκατέροις ἤρθη) as a signal for beginning action[339].
Thucydides mentions two other instances[340] in which a fleet awaited the signal before commencing to fight, but the only strictly tactical signal which he has recorded was one made to the Peloponnesian fleet in 429 b.c. The Peloponnesians had enticed the Athenian fleet into a disadvantageous position by a feigned attack upon Naupactus. At a given signal (ἀπὸ σημείον) the Peloponnesians suddenly turned their ships round and attacked the Athenians[341].
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) 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) he says:
39. Let there be some standard (σημεῖον) in your ship, either a banner (βάνδον) or a streamer (φλάμουλον) 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.
40. For in such an emergency you will not be able to make use either of the voice or of the trumpet to communicate what is necessary, because of the uproar and the tumult, and the sound of the sea, and the crash of ship against ship, the noise of the oars, and above all the clamour of the combatants.