1200 BC: Fire signals used at the siege of Troy
776 BC: First document use of pigeons, announcing the Olympian winner to the people of Athens
200 BC: Egypt and China use messengers on foot and on horseback, using relay stations
150 BC: Greek historian Polybus converts the Greek alphabet to numeric, enabling coded texts to be signaled
37 AD: Heliographs – Roman Emperor Tiberius uses mirrors to communicate with his empire
1608: Telescope invented, enabling ships at sea to use signal flags
1793: Mechanical semaphores on hilltop towers used by Claude Chappe in France