It was again visited, seven years later, by fire, from which it had hardly recovered when a third conflagration occurred and left traces of devastation for ages. In 1141, Robert Earl of Gloucester was placed in the Castle. He was the chief general and counsellor of Matilda, and had been captured prisoner at Winchester after having effected the Queen's escape. He was eventually exchanged for King Stephen. In 1215 the barons seized and held the Castle against King John, who gained it. Henry III. repaired the Castle. The Castle was again, in 1254, successfully defended for the King by Edward Earl Warren, against Simon de Montford and the barons. In the reign of Richard II. the insurrectionists under Wat Tyler released one of their comrades imprisoned in the Castle. Rochester has been at different times visited by reigning princes. Henry VIII., with Emperor Charles V., came there in 1521, whilst in 1573 Queen Elizabeth honoured it with her presence. Charles II., on his restoration, passed through the city _en route_ from the Continent to London. In fact Rochester, being also a port, was a convenient place for James II. to embark secretly on board of a trading-vessel lying in the Medway, by which he was conveyed to France. This Norman castle, which has played such an important part in the history of the city, deserves some notice. Its extensive remains, situated on a commanding site, overlook the right bank of the river. The Castle is supposed to have been built by Gundulph, when Bishop of Rochester, in the latter part of the eleventh century. It preceded by a few years the building of the Cathedral by the same prelate. The architecture of this castle is a striking example of the simplicity of plans generally employed by the Normans. By preference the castle was a rectangular keep in form. The sides varied from twenty-five to a hundred feet in length, and equally so in height. At the corners the walls advanced so as to form square towers, the faces of which were usually relieved by flat pilaster-like buttresses. The walls at the base measure sometimes as much as thirty feet in thickness, and diminish to as much as ten feet at the summit. The internal arrangements consisted of a store-room, from which a narrow staircase, made into the thickness of the walls, gave access to the rooms of the garrison and those of the owners above, wood being employed for the floor and roof. A well was always dug. The entire building was surrounded by a deep moat filled, if possible, with water. The entrance was small, and was defended by a draw-bridge and portcullis. It was on the thickness of their walls and the moat that the Normans chiefly relied for their impregnability. They seldom departed from this simple form of architecture. Their defence was rarely constructed on a series of fortifications. Local advantages and a lofty site were invariably the Norman idea of a safe stronghold.