Note 97 — Chapter I · NAVE AND AISLE VAULTS
Reading edition
Lasteyrie is of the opinion that these walls were raised to make it possible to place straight wooden beams across the church above the vaults (see Lasteyrie, p. 340, and also Choisy, II, p. 162, Fig. C.), but even if this were one reason, they also materially aided by their downward pressure, in offsetting the outward thrust.