There are two divisions: the outer ward, and the inner ward. William Rufus erected the keep, which was at first the only building on the site, and this was enclosed by a wall on the north and east. A triangular ward was thus formed, having its entrance at the south-east. Carlisle was fortified in 1170, and the city walls were carried up to the castle. At this time the first entrance was blocked up and the present one made; the outer ward was also enclosed. The south wall, with its flat buttresses, is partly Norman, and partly thirteenth-century work; and this description generally applies to the north and west walls. About 50 yards from the south-west angle and on the city walls is King Richard's Tower, a building of two storeys, where Richard III. is said to have lived when at Carlisle. It is also called the Tile Tower because of the thin bricks with which it was built. A subterranean passage leading to the keep was discovered here early this century. Entrance to the castle is gained by a bridge crossing the moat; this has replaced the old drawbridge and leads to a gatehouse with battlements, a kind of barbican, of two storeys. The passage is vaulted, and has massive doors of oak studded with iron; formerly there was also a portcullis. This leads to the outer ward which is about four times as large as the inner ward. It is nearly square, and contains modern buildings for the use of the garrison. The two wards are divided by a strong stone wall 90 yards in length. A wide ditch (now filled up) once ran in front. In the centre of this wall is a building--the Captain's Tower--which gives access to the inner ward through its gateway secured at each end with a strong door. Some of the masonry of the Captain's Tower is Norman, but it is mostly Decorated. A half-moon battery of three guns once defended the Tower and commanded the outer ward, but it has now been removed. [Illustration: PLAN OF THE CASTLE (TIME OF QUEEN ELIZABETH).]