posted 04-01-99 04:34 PM
The foundations of most British stone castles are very shallow, a couple of meters at most, and would have required no special digging tools beyond a common spade. Few castles have underground cellers (and fewer still have underground prisons) and of those few that do most of these are a result of the earth being raised around the castle after it was built on firm soil.The spade itself is was a few simple ancient tools little changed until recent times. The Bayeux Tapestry depicts two types being used to build Hastings castle. A pointed digging spade with a step so that a foot can be put on it to press it into the ground and a round headed spade, rather like a large spoon, used to shovel the earth around. These two spades would almost certainly been entirely wood. (I think Ash was a popular wood for tool making but I may be wrong with this). Later spades were reinforced with iron on the cutting edge. Totally iron headed spades are rare before the 19th century.
Also in the Bayeux Tapestry a man is depicted using a deers antler as a pick to loosen the soil for the spademen. I think that simple pointed sticks were probable also used in this sort of way.
Basically foundations were simple, relatively shallow, trenchs dug a few feet, into the firm soil, by peasants using the simple gardening tools that each peasant would have had readily to hand to dig his own vegetable garden. The walls would have then been laid straight onto the firm ground, or onto a base of a rammed hardcore of assorted rubble, stone and timber. The structral stability of the building came from the great mass of the walls themselves.
Castle foundations were, not suprisingly, known to fail and some castles did just fall down after quite short periods. The shallow foundations did also make castles suseptable to undermining during seiges (Notable at Rochester Castle) but the techniques of deep foundations did not exist so this was only avoidable where a castle could be built onto solid bedrock.
Those castles that were built onto solid bedrock had no special foundations but the bedrock would have been prepared by quarrymen and masons using iron cold chisels, wooden wedges (inserted into cracks and soaked so as to swell and split the rock) and other such techniques like fire cracking (where a fire is laid against a rock to heat it up then the rock is suddenly cooled with water and cracks because on the sudden contraction)