forming two sides of its perimeter, and probably broken through where the ditch infringed upon it at either end. With the sole exception of Colchester keep, which, as will be seen from the following table of dimensions, is considerably larger, the tower or keep of the castle of London exceeds in size the great rectangular keep of every other castle in the British Isles. Unfortunately, the two upper stories of Colchester keep have been destroyed, but sufficient remains (coupled with the resemblance of its plan to that of the White Tower) to show that both were designed by the same hand and erected about the same period, while both alike were royal castles. TABLE OF COMPARATIVE DIMENSIONS LONDON. COLCHESTER. Length (North to South) over all 121 feet 170 feet Ditto within Buttresses 118 " 153 " Breadth (East to West) over all 100 " 130 " Ditto within Buttresses 98 " 115 " Breadth of Apse 42 " 48 " Diameter of Apse 21 " 24 " Length (on South Side) over all 128 " 153 " Number of Stories 4 now 2 Total Height 92 feet --- Height of Two Lower Stories 42 " 32 feet Thickness of Walls 15 " 14 " Thanks to the drastic removals of recent years, the White Tower stands to-day very much as when first erected. In plan it is practically rectangular, but the north-east angle is capped by a projecting circular turret containing the great main staircase that ascends from the basement to the roof, serving each floor _en passant_, while the south angle of the east face has a large semicircular projection that contains the apse of the chapel. The main staircase terminates in a large circular turret of two stories, that rises some twenty-nine feet above the roof. The other angles terminate in three rectangular turrets about fourteen feet square, and twenty-seven feet high above the roof. The walls are at the base some fifteen feet in thickness, exclusive of the steep battering plinth from which they rise, and which slopes sharply outwards. They diminish by set-offs at each floor. The interior is divided into two unequally sized chambers by a cross-wall ten feet in thickness, running from north to south. Of these, the eastern one is again subdivided by a thick cross-wall at its southern end, which is carried up solid to the roof, while on the upper floors the central wall is perforated by arcades of three, and four perfectly plain semicircular headed arches. To the north and west the basement floor is about sixteen feet below the existing ground level, which falls rapidly along the east side, and on the south it is practically on the ground level, as the ground there has not been artificially raised. The two larger chambers