Ambulatories with Transverse Tunnel Vaults
The gallery of the Palatine chapel at Aachen is covered in still another manner by a series of ramping tunnel vaults alternately triangular and square in plan and springing from a series of transverse arches. Although never exactly copied in ambulatory vaulting, a similar system in which ramping groined vaults displace the simple tunnel form appears in the gallery of the north transept of San Fedele at Como (twelfth century)[418] while the system of ramping the vault had still another application in the trapezoidal groined vaults of San Tommaso at Almeno-San-Salvatore,[419] the evident object being to get a slant above the vaults suitable for an exterior roof which might rest directly upon them. But if ramping tunnel vaults were not used over the ambulatory, there are at least two instances of the employment of expanding transverse tunnel vaults in this position and these may well be products of the Aachen type. The ambulatory at Vertheuil[420] affords an example dating from about the middle of the twelfth century, which must soon have been followed by the gallery of the cathedral of Notre Dame at Mantes (beg. in 1160?).[421] Here the vaults are similar, but on a much larger scale, and with quite different transverse supports consisting of lintels, each resting upon two columns placed between the apsidal piers and the outer walls. [422]