The Spectator at war: Attack and defence

From The Spectator, 3 October 1914:

The essential value of a fortress is to act as an anvil upon which the field army, or relieving army, outside, which is the hammer, may pound the assailants to atoms. If there is such an army out- side, the parts are reversed—the besiegers, since they must stick to their position, become, as far as the relieving army is concerned, the besieged. It is the relieving army which can choose the place to hit and the time to hit. Unless the besiegers should prove to have enough troops to push it off and drive it away, the field army, when it gets to the proper distance, will strike the iron on the anvil and break it in pieces.