226 COMPARATIVE ARCHITECTURE. and 105 c). They are either square, octagonal, or circular, with well-marked stories, having windows to each, and are placed at the west and east ends and the crossing of nave and transepts. B. Walls. — Roman work and precedent, of course, influenced all constructive art in Europe, although technical skill was at a very low ebb during this period. Walls were in general coarsely built, having on the exterior, buttresses formed as pilaster strips of slight projection^ connected at the top by horizontal mouldings, or by a row of semicircular arches resting on a corbel table projecting from the wall. Semicircular arches, resting on rudely formed capitals, also occur. Other peculiarities are referred to in the comparative table of each country. c. Openings. — The door and window openings are very characteristic. The principle upon which the jambs were formed was in receding planes, or rectangular recesses, known as " orders," in which were placed circular columns or shafts. The arches followed the same method, being built in concentric rings (No. 94 f, h, j). A continuous abacus often occurs over these columns, and the profile of the jamb is carried round the semicircular portion of the arch in southern examples. The principal doorways are usually placed in the transepts. The characteristic rose (or wheel) window occurred over the principal door of the church in the west front, as at Iffley Church, Oxon (No. 138) ; also in Southern Italian examples, as at Palermo. D. Roofs. — The general employment of vaulting, especially over the side aisles in the eleventh century, was due to the desire of fire-proofing the building, but the central nave was still often covered with a plain wooden roof. The form of arch universally employed was semicircular (No. 94 a), often raised, i.e., stilted (No. 112 d', g). In early examples rib mouldings were not used in the vaulting, but when introduced, about iioo a.d., were at first plain, and afterwards moulded in a simple manner (No. 94). Intersecting barrel vaults (No. 112 g) were usual, and the difficulty in con- structing these in oblong bays led to the use of pointed arches in later times. When the crossing was crowned by an octa- gonal dome, four of the sides were carried on "squinch " arches (Nos. 94 and 105). The Romanesque architects used " flying buttresses " under the aisle roof, in the case where the thrust of a vaulted roof had to be met (Nos. 94 and 100) ; but it was left for the Gothic architects of the thirteenth century to place them above the aisle roof and weight them with pinnacles. E. Columns. — The shafts of the columns have a variety of treatments, flutings being used (Nos. 98 b, 107 l), of vertical, spiral, or trellis work form, or the whole shaft is sometimes covered with sculptured ornaments. In early examples forms of the Corinthian or Ionic capitals occur — as in the third column from
