JAPAN
finally the donjon itself. This last, which had a base more than one hundred feet square, stood on a battering stone basement forty-eight feet high, access being by means of stone steps and platforms with projecting walls and battlements. The donjon was three-storeyed, over forty feet high. Its framework was of timbers, huge in scantling, and these were covered externally with a thick coating of clay plaster as a protection against fire. The granite blocks used in constructing the basement of the donjon, as well as those in the basements of the gates and turrets and at the corners and angles of the escarpments, were of huge size. Many of them measured fourteen feet in length and breadth, and some attained a length of twenty feet. These immense stones had to be conveyed by water from quarries at a distance of several miles. The moats were crossed by wooden bridges constructed so as to be easily destroyed by the garrison in case of emergency, and the main bridge was built in such a manner that by the removal of a single pin the whole structure would fall to pieces,—a fact from which it derived its name, "abacus bridge." It could thus be used by the garrison till the last moment. Each gate opened upon an inner court surrounded by a high parapet, from which a cross fire could be poured upon the enemy after he had forced the gate, as well as upon the bridge leading to the gate. In short, an assailant, having broken through the massive iron-bound timbers of an outer gate, found himself, not within the enceinte,
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