_The Tower of London._--This great fortress, palace, and prison, unique among the castles of England, dates from the time of William the Conqueror. The site occupied a position upon the river Thames immediately to the east of Roman London; the latter was surrounded by massive walls with mural towers which had subsequently been repaired by Alfred the Great. A portion of this walling undoubtedly furnished part of the western defence of the Norman citadel, inasmuch as remains have been found adjacent to the present Wakefield Tower. The wall thus adapted extended between two bastions, and possibly the first enclosure was merely stockaded. It was, however, necessary to erect a more substantial fortress in order to overawe as well as protect London, and in 1078, William entrusted Gundulf, the architect-bishop of Rochester, with the commission. The great Keeps at Rochester and West Malling were also designed by him, and possibly he had much to do with those at Norwich, Colchester, and other places in England. To this period may also be ascribed some of the towers and part of the massive curtain wall lying to the west of the inner ward or ballium which at that period contained the royal palace, apartments for the court, and dwellings for the garrison. Possibly a narrow ditch encircled the walls on the inner line of the present spacious moat. In 1155, the buildings were repaired by Thomas à Becket; but to Richard I. must be ascribed the carrying out of works which materially added to the general strength. Henry III. caused additions to be made, chiefly upon the river front, which give it the characteristic appearance it presents at the present day. The well-known Traitors' Gate dates from this period, and is one of the finest examples of medieval masonry in existence. About the year 1270 the Tower began to acquire those features which subsequently rendered it an excellent example of the concentric fortress; an outer wall of circumvallation was carried completely round, with a deep and broad moat washing its face. The outer ward was formed lying between the two lines of walls, thus producing three lines of defence, the innermost being the great Keep. A small barbican, which has now disappeared, stood upon the outer edge of the moat. In the early part of the reign of Edward III. some towers were added, the chief being the Beauchamp and Bowyer. Since the period of the Commonwealth the Tower has ceased to be inhabited by royalty, the removal of the palace, which stood against the south-eastern corner of the inner ward, being probably responsible for it. As the Tower of London has been inextricably involved in the major portion of events forming the history of England, it is obviously impossible to deal even in a cursory manner with them within the confines of this work. A few facts, however, relating to the Keep may be of interest, as it is undoubtedly the most ancient portion of the structure. It is rectangular in shape, 118 feet long by 107 feet