Aggressive weapons of war and violence represent some of our earliest technological shelves, followed by corresponding defensive technologies developed later by communities for protecting their goods and themselves with walls and by building cisterns in order to ride out attacks and sieges. Little was different in the Graeco-Roman period when most cities were protected by defensive walls. As an integral part of life, military affairs dominate a large part of classical literature with extensive information from Xenophon (fourth century bc) to Frontinus (first century ac), Vegetius (fourth century ac), and later. The texts of this chapter relate the social status, tactics, and armour (leather, chain-mail, head, breastplate, greaves, shield), and weapons (sword, pilum, javelin, spear) of cavalry (horses, elephants, cataphracts), of the Greek hoplite phalanx, and of the Roman legionary units of deployment. The texts further provide information about military camps, fortifications, siege-machinery (ballistae, catapults, onagers, and rams) and siege-tactics (tortoise, towers, sappers, and divers) with a section on ciphers and signals. Texts regarding the corvus and the siege-machines of Archimedes appear in this chapter, but those concerning naval military vessels appear in Chapter 11.