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C-. .-= ,- -._ ::: .• ••• the nave and aisles of Sant' Ambrogio ,"£? ^iui i_ I were divided in the usual way with ! *^^T ^^ / ^"" arcades, and were covered with open timber roofs. In the rebuilding of the church (fig. 35) the nave (38 ft. wide) was divided into four square bays, and compound piers of large dimensions were built, to carry the transverse and diagonal ribs of the new vault. To resist the thrust, the walls across the aisles were built up to the roof, and had external buttresses; the diagonal ribs, instead of following the elliptical curve which the intersection of the Roman semicircular barrel-vault gave to the groin, were made semicircular, so that the web or vaulting surface which rested on these ribs rose upwards towards the centre of the bay, giving a distinct domical form to the vault. The aisles, being half the FIG. 35.— Plan of S. Ambrogio. width of the nave, were divided into eight compartments, two to each bay of the nave, and were covered both in the ground storey and the triforium with intersecting groin vaults. When this rebuilding took place, the front of the church was brought forward, bearing a narthex, and the arcades of the atrium were rebuilt in the first years of the I2th century.

The triple apse, to the external decoration of which we have called attention, the crypt underneath, and the south campanile, are the only remains of the 9th century church. The campanile on the north side was built 1 125-1 149, and the decoration with pilaster strips, semi-detached shafts, and arched corbel table, is repeated on the facade of the church and on the arcade round the atrium. In the rebuilding, portions of the sculptural decoration of the 9th century church were utilized; this would appear to have been a Lombard custom, as in the church of San Michele the lower part of the main front is encrusted with sculptured decoration taken from the earlier churches built on the site. These ancient sculptures are of special interest, as they constitute the best records of the rude Lombard work of the 8th and gth centuries, and are intermingled with Byzantine scroll work and interlaced patterns. If the plan of Sant' Ambrogio, with its comparatively thin enclosure walls, suggests its original construction as an ordinary basilica, this is not the case with San Michele (fig. 36), where all the external walls are of great thickness.showing that from the first it was intended to vault the whole structure.

The church is much smaller than Sant' Ambrogio, there being originally only two square bays to the nave (in the isth century the vaults were rebuilt with four bays) ; the transept, however, projects widely beyond the aisles, and as there is another bay given to the choir in front of the apse, the area of the two churches is about the same. The existing church was FIG. 36. — Plan of San Michele, Pavia. probably begun shortly after the destructive earthquake of 1117, and was consecrated in 1132. In Sant' Ambrogio the transverse and diagonal arches spring from just above the triforium floor, so that there was no room for clerestory windows, and consequently the interior is dark. In San Michele the ribs rise from the level of the top of the triforium arcades, and two clerestory windows are provided to each bay. The crossing of the nave and transept is covered with a dome, carried on squmches, which dates from the first building. The dome over the fourth bay of Sant' Ambrogio replaced the original vault about the beginning of the I3th century.

The cathedral of Novara, originally of the ordinary basilica type of the loth century with timber roofs, was reconstructed in the nth century, compound piers being built to carry the transverse and diagonal ribs, and walls built across the outer aisles to resist the thrust; on the other hand SS. Pietro and Paolo at Bologna is a I2th century church, which was designed from the first to be vaulted. To these, and still belonging to the basilican plan, must be added San Pietro in Cielo d'oro (1136) and San Teodoro, both in Pavia; S. Evasio at Casale-Monferrato, having a comparatively narrow nave with double aisles on either side and a very remarkable narthex or porch: S. Lorenzo at Verona (lately restored), which in the I2th century was rebuilt with compound piers to carry a vault (the apse and the two remarkable circular towers in the west front belong to the ancient church); and Sant' Abbondio at Como, often restored and partly rebuilt, retaining, however, some of the original sculpture of the early Lombard period. Of churches built on the plan of the Latin cross, examples are Sant' Antonino at Piacenza, with an octagonal lantern tower over the crossing; Parma cathedral (c.

1 1 75). with an octagonal pointed dome over the crossing; Modena cathedral, rebuilt and consecrated