The Normans having secured a foot-hold in the country, commenced at once to make their tenure secure, and to establish their power. This they accomplished with wonderful skill and success. NORMAN COAST CASTLES The castles first built in England by the Normans consisted of palisaded earthworks, the main feature being a lofty but truncated mound encircled by a deep ditch, and closely related to it were generally two courts or baileys. They were built in such situations as would command rivers and important roads, and so dominate the English people. Usually the castles of this period were built just within the boundaries of walled towns. The relation of the Tower to the City of London affords an excellent example of this arrangement. Primarily the purpose of the Norman castle was to complete the work begun at the Battle of Hastings of subjugating the native population of England, and it is believed that castles of this type were employed for this purpose, because of the ease and rapidity with which they could be thrown up. Castles of this type were erected in England, not only after the Norman Conquest but also before it, and at one time the idea was generally held that they represented the usual and normal species of defence employed in Saxon times. The late G. T. Clark, who was a pioneer in the scientific study of English and Welsh castles, considered that these works were the actual burhs of the Anglo-Saxons, so often mentioned in the "Anglo-Saxon Chronicle." The theory was generally accepted for some years, but in due course doubts were cast upon it by the researches of Dr. J. Horace Round, Mrs. E. S. Armitage and others. It is now generally held that those examples of this type of defence which are known to have been constructed before the Conquest were built under the influence of Edward the Confessor's Norman friends. England at that time was following the fashions of Normandy; but the great majority of defences of this type were built, probably, very soon after the Norman Conquest, and under the direct influence of the Norman Conquerors. It is worthy of note that numerous examples exist to this day in Normandy, and some, with the characteristic palisaded mound, are represented in the Bayeux tapestry. In many cases the earthwork castles as first built were, in due course, rebuilt in stone, the top of the mound being capped by a shell-keep and the other eminences being surmounted and reinforced by walls. Another type of keep, generally square in plan and of great strength and size, was built, as at Dover, Rochester, Canterbury, London, etc.; but such massive structures required firm foundations, and they were always built on undisturbed sites. These two kinds of keeps practically determine the two types into which the Norman castles built in England naturally fall.