In an invasion of the British Isles at the present day the unwelcome intruder would probably hasten to entrench himself and render his position safe by pits, earthworks, and an elaborate entanglement of barbed wire; and in the same manner as these could be rapidly prepared, so we find that the Conqueror, directly after Hastings, threw up the defence which would be the most expeditious in the making and the cheapest in construction. The Motte and Bailey castle fulfilled both conditions inasmuch as it was only necessary to obtain, by fair means or otherwise, an adequate number of Saxon labourers to ensure the rapid erection of the mound, while simultaneously the local trees were being felled and roughly hewn into shape by native carpenters for the palisades and bretasche. To give an idea of the speed with which these fortresses could be made, we find that in a brief campaign of less than two months, in 1068, the king founded eight of considerable importance, including those at Nottingham, Warwick, Lincoln, Huntingdon, and York; in the following year the erection of a second castle at York only occupied eight days, and Baile Hill, the mount of the defence in question, sufficiently testifies to the magnitude of the work. One great advantage of the system should not be forgotten, namely, the possibility of adequate defence by a small garrison because of the narrow front exposed to an attack, and the immunity from harm of the besieged while the defences stood intact. _Windsor._--The Royal Castle of Windsor originated in one of the Motte and Bailey type erected by the Conqueror upon the striking eminence near the Thames. It was one of those that were hastily thrown up in order to consolidate his power, as it is mentioned as early as 1070, and in Domesday Book in 1086. It is one of a small and exclusive type by reason of the dominating motte occupying the centre of the enclosure instead of the usual position at the side or end; this peculiarity is shared by Arundel, Nottingham, and one or two others. It is quite reasonable to infer, however, that one, or even both, of the baileys were added at some time subsequent to the throwing up of the mound. It was sufficiently advanced in strength in 1095 to be the prison of de Mowbray, Earl of Northumberland, and the extensive additions made by Henry I. enabled the Court to be held there in 1110. John seized on Windsor during the absence of his brother, but was besieged in it by the loyal barons, and forced to surrender. Windsor has been stated as the place of imprisonment of the de Braose family in 1210, who were deliberately starved to death by the inhuman John. In the reign of Henry III. very extensive building operations occurred, and a number of towers, including the Barbican, were added, but probably Edward III. left a greater mark upon the castle than any monarch preceding him, possibly by reason of a natural affection for his birthplace.