It will readily be seen that this logical and reasonable mode of constructing arched openings would, when applied to arches carried on pillars, lead to the clustered column. If the wall was not thick, the arches might certainly continue to be of one order, and the most natural mode of supporting them would then, as heretofore, be single columns. Where, however, the wall was so thick as to give it a clumsy look if the arch ran square through it, it would be divided into two orders, and would assume at its springing a cruciform plan. The impost must break round this figure; and though the column might still remain (and often did remain) round (Figs. 141, 142), the abacus only assuming the cross form, the most natural thing would be to form a complex pillar composed of four shafts united in one, each apparently supporting its own order of the arch (Fig. 143). [Illustration: Fig. 141.] [Illustration: Fig. 142.] [Illustration: Fig. 143.] If the arch were divided into three orders, a more complex form suggested itself, containing eight shafts; and as the system was carried out, many other combinations arose not necessary to enumerate. Thus we see that the adoption of the arched system of construction, unbiassed by any pre-existing laws of art, but aided only by the very rational desire to utilise the materials most abundantly provided by nature, led to two of the most important characteristics common to Romanesque and Gothic architecture, viz., the sub-ordinated arch and the clustered column, with the whole system of decoration derived from them; than which no two features can be pointed out which have been more richly fruitful of architectural forms the most original and beautiful. Again, in the mode of bringing down the arch upon columns, the Romanesque builders exercised a sound discretion. The Greeks and Romans in their trabeated construction, reasonably enough, made their architraves only as wide as the upper diameter of their columns, so that whatever projection the capitals had beyond the shaft, they had the same beyond the architrave also. When, however, you substitute two arches for two architraves, you bring down the weight by two opposite forces; its footing on the capital, therefore, requires as much steadiment as possible.