In France the Romanesque column has usually a third of the diameter of its shaft engaged in a pier or wall, though isolated ones are used in the triforiums, towers, and porches; in England the latter are common, and recessed columns, that is to say, placed in an angle of masonry, are also frequently seen. The bases of Romanesque columns, at first simple round and hollow moulds, gradually became more elaborate, until they resembled the attic base. Occasionally they were decorated with foliage or animals, and there are instances where both capital and base are similar. The introduction of an angle ornament, connecting the torus or round mould with the corners of the plinth beneath, is especially noticeable; this was effective in preventing the angles from being broken by thickening the stone at the weakest points, and in later examples added to the beauty of the base. The arches of the period were usually semicircular and employed either separately or with a second and broader one, their contour being frequently marked by a few simple mouldings of degenerate classic origin. Two or three arches supported by detached columns, and comprised within a larger one, were frequently placed in the triforiums; when three were used the central one was usually higher than the others. Besides mouldings: billets, zigzags, stars, and similar simple ornaments were employed in their decoration. Where Arabic taste exercised its influence, it is not uncommon to find alternate voussoirs of different-coloured stones, and variegated bands in the piers. The Italians were especially fond of this treatment and it is seen in the exteriors and interiors of many of their buildings. To them is also due the introduction of blind arcades, the columns of which were either engaged in the wall or separated from it by an intervening gallery. The façade of the cathedral at Pisa is perhaps the most beautiful example of this. In the West, arcades of this kind became a frequent method of decorating blank walls, and there are instances where a second series of arches intersect the first, resulting in a number of pointed arches formed by the crossing of the circular ones; from this an ingenious but unfounded theory has been deducted purporting to explain the origin of Gothic architecture. The doors and porches of the Romanesque period are among the most beautiful to be found in any style. Starting in the earlier examples with a simple, round-arched opening, the number of mouldings in the arch became richer and of greater number, and, as the style advanced, recessed and supported by columns. These mouldings were decorated with the zigzag, billet, and kindred ornaments, many of which were probably copied from the decoration of the old basilica of St. Paul’s without the walls of Rome.