Aeneas Tacticus (; fl. 4th century BC) was one of the earliest Greek writers on the art of war and is credited as the first author to provide a complete guide to securing military communications. Polybius described his design for a hydraulic semaphore system. His only surviving work, How to Survive Under Siege, covers how to defend a fortified city that is under siege. The work gives instruction to not just military commanders but also the citizens of the city under attack, providing secure communication, internal security, and how to keep morale high. He also provides a lot of insight into the politics within the classical polis.
thumb|Part-title page of the first printed edition of Aeneas Tacticus, by [[Isaac Casaubon, an appendix to his edition of Polybius (Cologne, 1609)|left]]
According to Aelianus Tacticus and Polybius, he wrote a number of treatises () on the subject. The only extant one, How to Survive under Siege (, ), deals with the best methods of defending a fortified city. Aeneas describes how one should choose trustworthy guards to maintain the secure communications to detect internal conspiracies, as well as simpler tactics like securing the surrounding walls and gates.
Aeneas was considered by Isaac Casaubon to have been a contemporary of Xenophon and identical with the Arcadian general Aeneas of Stymphalus, whom Xenophon (Hellenica, vii.3) mentions as fighting at the Battle of Mantinea (362 BC). Through his writing you can see the correlation between defensive challenges and political instability within the Greek city-states during the 4th century BC. This shows he had experiences in domestic security or civic defense.
Aeneas's treatise sustained its influence with writers on military theory after his time. Aelianus Tacticus and Polybius both refer to him as a pioneer on communication and military tactics, showing the value others had on his observations.