During the period between 1931 and 1933 Dr. P.G. Laver made several investigations into the Castle Keep. In 1931 a north-south section was cut 'with great difficulty' in the small prison. It was made through a limited gap in the Norman tile floor.<1> The exact dimensions of this excavation are unknown. In 1932 Trenches cut by Laver <2> included one at right angles to the east wall of the keep, immediately south of the existing doorway. This revealed a drain-pipe and robbing of the Roman work. Two other trenches were cut up to the west face of the remaining Norman partition wall and revealed the temple podium and in 1933 a long east-west section was excavated through the sub-crypt 'small prison'. Again, the dimensions of this excavation are unknown.<3>