Prearranged signals were used to convey news in even earlier times.  Fire, smoke, and flags were used by the Egyptians and the Assyrians previous to the Trojan War.  The towers along the Chinese Wall were more than watch-towers; they were signal-towers.  A flag or a light exhibited from tower to tower would quickly convey a certain message agreed upon in advance.  Human thought required a system which could convey more than one idea, and yet skill in conveying news grew slowly.

Perhaps the earliest example of marine signaling of which we know is recorded of the Argonautic Expedition.  Theseus devised the use of colored sails to convey messages from ship to ship of the fleet, and caused the death of his father by his failure to handle the signals properly.  Theseus sailed into conflict with the enemy with black sails set, a signal of battle and of death.  With the battle over and himself the victor, he forgot to lower the black flag and set the red flag of victory.  His father, the aged AEgeus, seeing the black flag, believed it reported his son’s death, and, flinging himself into the sea, was drowned.

In time it occurred to the great monarchs as their domains extended to establish relays of couriers to bear the messages which must be carried.  Such systems were established by the Greeks, the Romans, and the Aztecs.  Each courier would run the length of his own route and would then shout or pass the message to the next runner, who would speed it away in turn.  Such was the method employed by our own pony-express riders.

An ancient Persian king thought of having the messages shouted from sentinel to sentinel, instead of being carried more slowly by relays of couriers.  So he established sentinels at regular intervals within hearing of one another, and messages were shouted from one to the other.  Just fancy the number of sentinels required to establish a line between distant cities, and the opportunities for misunderstanding and mistake!  The ancient Gauls also employed this method of communication.  Caesar records that the news of the massacre of the Romans at Orleans was sent to Auvergne, a distance of nearly one hundred and fifty miles, by the same evening.

Though signaling by flashes of light occurred to the ancients, we have no knowledge that they devised a way of using the light-flashes for any but the simplest prearranged messages.  The mirrors of the Pharaohs were probably used to flash light for signal purposes.  We know that the Persians applied them to signaling in time of war.  It is reported that flashes from the shields were used to convey news at the battle of Marathon.  These seem to be the forerunners of the heliograph.  But the heliograph using the dot-and-dash system of the Morse code can be used to transmit any message whatever.  The ancients had evolved systems by which any word could be spelled, but they did not seem to be able to apply them practically to their primitive heliographs.