Krios (κριός). The battering-ram, one of the most effective engines used by the ancients to make a breach in the walls of a besieged town. Originally it consisted of a strong pole, with ironmounted head, brought up to the wall in earlier times by hand, in later times on wheels. In its final form it was constructed in the following manner: A stout beam, sometimes composed of several pieces, and measuring from sixty-five to one hundred feet long or more, was hung by ropes on a strongly mounted horizontal beam, and swung backwards and forwards, so as to loosen the stones of the wall and make it fall. As the engine stood close to the wall, the men working it were sheltered by a roofed shell of boards, called the ram tortoise-shell (testudo arietina) and resting on a framework that ran upon wheels. To protect the roof and sides of the shell against fire thrown from the walls, they were coated with raw or well-soaked hides, or other similar contrivances. The loosened stones were picked out of the wall with a strong iron hook at the end of a pole— the wall-sickle (falx muralis), as it was called. Single holes were punched in the wall with the wall-borer (terebra), a ram with a sharp point, which was pushed forward on rollers.

The besieged tried to knock the ram's head off by dropping heavy stones on it, or to catch it in a noose and turn the blow aside or upwards, or to deaden the force of its blows with sand-bags and mats. By the usage of war, a town that wished to secure indulgent treatment must surrender before the ram touched the walls.