Attention has already been drawn to the earliest fortifications in the county. They were banks of earth and had probably wooden palisades. In Norman times fortified residences became common and were usually of stone. The history of a Norman castle was probably often as follows. In the first place a tower called a "keep" was built and was protected by a moat and probably by some earthworks. Then at a later date the earthworks were replaced by walls, which usually enclosed a larger space than the older fortification. The walls were usually strengthened by towers, but the keep still remained the citadel of the fortress. We know that William the Conqueror built a castle on the chalk hill at Windsor before the year 1086, but we know nothing of its plan or form, for no part of the present castle can be dated before the reign of Henry II, and even of that time there are only the foundations and part of the lower story on the south side of the Upper Ward. The imposing western wall of the Lower Ward, with its three towers, belongs to the time of Henry III. The Round Tower on its high mound is the keep of the castle, and much of it is as old as the time of Henry III. The top part, however, is modern. Close to the Round Tower is an old Norman gate which was rebuilt by Henry III and again by Edward III. The gateway could be closed by doors and also by a portcullis or grille let down from above, and the portcullis is still in its place ready to be lowered. The view of Windsor Castle given on p. 2 is taken from the Buckinghamshire bank of the river Thames and shows the north side of the castle. On the left are the buildings which contain the state apartments; in the centre is the Round Tower. To the right we see St George's Chapel with its great west end window, and still further to the right is the Clewer or Curfew Tower with the pointed roof. The main part of this tower dates from Henry III, and it has been used as a bell tower since the time of Edward III. The pointed roof is modern. St George's Hall (p. 78) is in the part of Windsor Castle known as the State Apartments, and in it the feasts of the Knights of the Garter are held. It is an old hall, but was much altered by Sir Jeffry Wyatville, the architect employed by George IV to repair the castle. There was nearly always a well in the keep of a Norman castle, and this was the case at Windsor, the well in the Round Tower being 160 feet deep. There is a great rectangular earthwork at Wallingford which may go back to Roman or early British times, but in any case it was adopted by the Normans and a castle was built on the site. The mound on which the keep was built still exists, but little else of these buildings survives.