THE MEDIEVAL CATHEDRALS 421 strengthened to resist the outward thrust of the arches by projecting pilaster strips which formed solid buttresses resting directly upon the ground. The churches of Rome, central Italy, and Tuscany kept j the closest to the old columnar basilica, as we may illustrate i by the cathedral at Pisa, perhaps the finest Thecathe- I Romanesque church in Italy. It has transepts, a dral at Pisa lengthened choir, and great height, and an elliptical dome I over the crossing of nave and transepts. But the main body of the building is covered with a wooden roof and there are ( bare pent-roofs over its double aisles. Like the basilicas at I Ravenna, it has a detached round campanile, the famous J leaning tower. In the half-dome of its apse is a mosaic, I and sixty-eight classical columns taken from older buildings I carry the arcades on which the walls of its nave rest. The exterior, however, has some Romanesque features common to churches of this period and which relieve the monotony of i its plain walls, although at Pisa these would be beautiful I anyway, owing to the golden, creamy marbles of which they I are built. First, pilaster strips project at frequent intervals ' from the wall and carry a blind arcade or series of engaged round arches. Secondly, the exterior wall surface is inter- rupted at certain places by open colonnades, which are set in it, and which are composed of small columns with connect- ing arches and with an open gallery between them and the blank wall behind. The favorite place for such dwarf gal- leries was just under the eaves of the roof and especially around the curve of the apse, but at Pisa there are two colonnades one above the other on the apse, four rows form the upper part of the facade, while the leaning tower is encircled from top to bottom with such colonnades. In northern Italy more of an effort at vaulting was made, but it was especially in the Romanesque building of south- ern France and of the Cluniac monks in Bur- Experiments gundy that all sorts of attempts were early made in vaultin e to solve the problem of a stone roof. Sometimes the archi- tects tried a series of small domes or cupolas over different sections of the church ; sometimes, plain round vaults ; some-
