A castle in that place and time was a little town in itself, and it must be able to exist by itself when necessary, without markets or factories or outside help of any kind. Like most Normans the knight was a born builder, and had taken care to make his castle as proof against attack, and as scientifically built, as castle could be. Each landowner had to be his own architect. Certain general rules were followed, of course. The keep, the fosse, the inner and outer bailey, the general construction, were much the same in all fortresses of Normandy or Norman Britain. But no two sites were alike, and the work had to be planned not only according to the shape of the hill but with reference to the material to be had, the amount and quality of labor at hand, and the climate. This castle was on a hill not high originally, but made some fifty feet higher by heaping up earth and stone to bring the whole top somewhere near the level of the huge rock on which the keep was built. On that side the river flowed almost under the precipitous western face of the mount, so that a stone could be dropped from the battlements into the water. The young page, Roger, thought he could fish from his window if he could get a line long enough. The keep was still the living-place of the family, but the double line of stone wall encircling the mount was finished, and at exposed points small watch-towers were placed, known as the mill-tower, the armorer's tower, the smith's tower or the salt-tower, according to their use. If the castle should be attacked each one of these outworks would be the post of a small garrison and stubbornly defended, while the keep could be held almost indefinitely. The deep cellars would hold grain and salt meat enough for months, and there was a spring within the walls. Even the narrow windows were so shaped that an arrow aimed at one of them would almost certainly strike the cunningly-sloped side and rebound, instead of entering the building. The gate was of massive timbers held together by heavy iron hinges and studded with nails, and above it was a projecting stone gallery connecting the two gateway towers. This gallery was machicolated, or built with a series of openings in the floor, through which the defenders could shoot arrows upon the besiegers, or pour boiling pitch down upon them. This was a Saracen contrivance, and had been suggested and supervised by Sir Hugh l'Estrange, who had seen the like in Spain. There was one place where all plans had gone wrong, and that was a part of the wall near the keep, almost under the windows of the well-chamber. It had been built three times, and always, before it was done, the stones would begin to slip and sink. Yesterday a section of wall had gone clean over into the river and carried a mason with it. Fortunately he could swim, and though nobody thought he would come out alive, he had scrambled up the bank very cold, somewhat bruised, and sputtering like a wet cat.