Note 211 — Chapter VII · THE PERIOD OF TRANSITION: CYLINDRICAL TOWER-KEEPS
Reading edition
On the third floor, these niches are divided into two stages and connected by an upper gallery which pierces the abutments of the vault, and surrounds the whole apartment. The method of vaulting this gallery behind the abutments, so as to give additional resistance to the masonry of the tower, is described by Lefèvre-Pontalis, op. cit. 94: see plan ibid., p. 93.