When one desired to attack the enemy's castle, there was a variety of ways one could go about the process. If the structure was only made of timber, the job was relatively easy. It could be battered, burnt, or bored through with a terebrus or teretrus. If, however, the lord had had the foresight to use stone construction, the walls of the curtains and towers were generally impervious to most assault tactics until the advent of artillery warfare.
The heel of the Achilles was used for mining under a castle. Although useless against castles built on a foundation of rock or an island, mining was especially effective by using the weight of the stones against the enemy. A tunnel would be built under the wall, and foundation stones would be removed. The castle was supported by timber beams so as not to collapse immediately. Then the timber supports would be fired, and when they collapsed so did the wall, leaving a wide gash through which the enemy could descend.
The 11th and especially the 12th centuries were the classic age of the keep. In England and France, most castles started as moat-and-bailey types, with shell walls added later to replace wooden palisades, and ranging from 40 to 150' long. In Germany, the Berg fried equivalent was a stone watchtower, less bulky than a keep, often built on the summit of a mountain these locations often meant for rather cramped accommodations.
After 1125, the tower-keep became more attractive to those building castles. With three or more stories to them, they would generally consist of a single floor on each story: a storage area on the ground floor, as with the hall-keep; the hall on the first floor; and the private chamber above on the second. The kitchen could be...