In the important additions made to the castle of Warkworth about 1400, the compromise attained between the requirements of defence and comfort is very striking. The plan of this castle, throughout its history, like the plan of Warwick, remained that of the original mount-and-bailey fortress. We have noticed already the addition of the stone curtain to the bailey, and the building of a large mansion against its western and southern faces. It is probable that a shell-keep was added to the mount, when the stone curtain was made; for the foundations of the present strong house on the mount are of masonry of an earlier and rougher character than the elaborately dressed stonework of the house itself. This house (221), which combines the features of keep and private residence in a most unusual way, appears to have been built by the first earl of Northumberland, who died in 1407.[355] The shape is that of a square with chamfered angles; but from the centre of each face projects a bold half-octagon, so that the ground-plan is a Greek cross with short arms and a large central block. The elevation consists of a basement and three floors. The basement contains tanks and a vault with a corbelled roof, which was certainly a prison, and bears a strong likeness to a similar vault in the inner gatehouse at Alnwick. There is no basement stair, communication with the vaults being through trap-doors in the floor above. On this floor are a number of dark vaulted store-rooms, one of which was the wine-cellar, and has its own stair to the daïs end of the hall on the floor above. The two upper floors are comparatively cheerful and well lighted: a shaft in the centre of the building gave light to the inner passage between the hall and kitchen. The main stair is in the south half-octagon, the chief doorway being in the west face of this projection, on the first floor. From the lobby on the second floor, at the head of the stair, two doorways open. That on the right leads into the hall, which occupies the south-east angle of the central block, and is of the full height of the two upper floors. That on the left leads to the servants’ quarters and the kitchens, which occupied the western part of the second floor, and communicated by separate doorways with the hall and chapel. The great kitchen filled the north-west angle of the central block, and, like the hall, was two stories in height. The north half-octagon and the north-east angle of the main block adjacent to it, were divided into two floors. The lower room in the half-octagon was probably the private room of the master of the house, communicating with the lower room in the main block, which was probably the common room of his immediate retinue. Similarly, upon the upper floor were a ladies’ bower and a separate room for the countess of Northumberland’s own use. Between the private apartments and the hall, occupying the centre of the east side of the main block and the half-octagon beyond, was the chapel. The chancel, in the half-octagon, was the height of both floors; but the western part of the chapel was in two floors, the upper forming a gallery, with a doorway from the ladies’ bower. From the south-east corner of this gallery, another doorway opened upon a narrow stone gallery, formed by the internal thickening of the lower part of the east wall of the hall: this may have served the purpose of a minstrels’ gallery, or may have been used by the ladies of the house, when they wished to watch the festivities below. The wall beneath this gallery is pierced by a long vestry or priest’s chamber, opening out of the south wall of the chapel, and built with a rising floor, in order to give head-way to the stair from the wine-cellar below. The ground-floor of the chapel also communicated with the hall and the men’s apartments. In addition to the rooms already mentioned, there were third-floor rooms in the south-west angle of the main block and in the western half-octagon, which communicated with the gallery of the chapel. The area covered is not large, but the ingenuity of the plan is remarkable; and the disposition of the various apartments must have required an amount of thought and skill, which no other medieval dwelling-house shows in so high a degree.