The first floor, like the basement, is divided into three rooms, as, in addition to the usual cross wall, the Tower has a branch cross wall to its eastern section, which is carried up to the top. This floor was formerly only lit by loopholes; Clark states that there were two fireplaces in the east wall, but there is some doubt about this. The S.E. room contained the crypt of the chapel, which was vaulted. It is commonly supposed that the rooms on the first floor were occupied by the guards of the keep. In the account which we have quoted from Lambert of Ardres, the first floor is said to be the lord's habitation, and the upper storey that of the guards; so that there seems to have been no invariable rule.[718] No special room was allotted to the kitchen, as in time of peace at any rate, the lord of the castle and all his retainers took their meals in a great hall in the bailey of the castle.[719] The ceilings of the two larger rooms of this floor are now supported by posts, an arrangement which is probably modern, as the present posts certainly are.[720] The second floor contains the chapel, which in many keeps is merely an oratory, but is here of unusual size. Its eastern end is carried out in a round apse, a feature which is also found at Colchester, but is not usual in Norman keeps.[721] It is a singularly fine specimen of an early Norman chapel. This floor probably contained the royal apartments; it was lighted by windows, not loops. Both the eastern and western rooms had fireplaces; the eastern room goes by the name of the Banqueting Chamber. The third storey is on a level with the triforium of the chapel.[722] This triforium is continued all round the keep as a mural passage, and it has windows only slightly smaller than those of the floor below. These mural galleries are found in most important keeps. As their windows were of larger size than the loops which lit the lower floors, it is possible that they may have been used for defence, either for throwing down missiles or for shooting with bows and arrows. But no near aim could be taken without a downward splay to the window, and the bows of the 11th and 12th centuries were incapable of a long aim. A plausible theory is that they were intended for the march of sentinels.[723] The masonry of the Tower is of Kentish rag, with ashlar quoins. In mediæval times it had a forebuilding, with a round stair turret, which is shown in some old views; but it may reasonably be doubted whether this was an original feature. As regards the ground plan of the castle as a whole, it is now concentric, but was not so originally. The Tower was certainly placed in the S.E. angle of the Roman walls of London, and very near the east wall, portions of which have been discovered.[724] The conversion of the castle into one of the concentric type was the work of later centuries, and the history of its development has still to be traced.[725]