This article concentrates on the role of technology in improving the operational capabilities of the Roman state. It reviews the organizational and weapon system developments that enabled Roman armies to engage their enemies with confidence in the field, alongside the evolution of fortification schemes that enabled economies of force, which were essential to imperial security. Roman weapons and equipment include the spear, sword, missiles, artillery, shields, helmets, and body armor. Although the Roman army was often on the attack and made use of complex siege technology, it was also highly skilled in the preparation of defensive fortifications. The Romans diligently applied themselves to the arts of war. Their successful mastery of battlefield techniques and their adoption, where appropriate, of equipment and technologies first introduced by their opponents allowed Roman armies to sustain the state over several hundreds of years of challenge and change.