Note 1194 — Chapter XII · STONE CASTLES OF THE NORMAN PERIOD
Reading edition
The walls of the Tower are from 12 to 15 feet thick at the base; those of Norwich 13; the four walls of Dover respectively, 17, 18, 19, and 21 feet; Carlisle, 15 feet on two sides. (Clark.) William of Worcester tells us that Bristol keep was 25 feet thick at the base! Itin., p. 260.