Simple as this step may appear, it is one whose importance can scarcely be over-stated; for it is the starting-point of the entire system of Romanesque and Gothic arch-moulding; it is the origin of the clustered columns, and the deeply-recessed and richly-decorated doorways which mark those styles; and to it we owe in great measure even the traceried windows which are such leading characteristics of Gothic architecture. For, as regards arches, we had before but one angle to mould, whereas we may now have as many as the thickness of our walls will permit, thus generating at once the great Mediæval system of receding orders, whether of arches or their jambs; and you will presently see that this gives us also our clustered columns, which are, in fact, the mere decoration of the receding orders of the piers. [Illustration: Fig. 286. Capital from the Crypt, Canterbury.] Let us now deal with such a pier as is shown in our last figure. It is clear that the plan of that pier is the same as that of the springers of the coupled arches which it supports, and that this plan is of a cross-form. It is not, however, necessary that this plan should be continuous through the pier, if only an impost is provided of a form suited to receive this double springer (Fig. 286). It is quite possible (and is very frequent), to substitute a single column for this cross-formed pier, giving it a capital whose abacus either assumes a like plan with the springer (Fig. 287), or, if either octagonal or round, is suited in size to contain it without either undue projection or much superfluous space. [Illustration: Fig. 287. Capital from Ely.] Let us, however, take another step; and instead of substituting a column for the group of arch-orders, let us substitute either a smaller column for each of the four orders, thus supporting the arches by a group of four columns (Fig. 288); or else let these be united into one complex pillar formed of portions of four columns (Fig. 289); or, thirdly, let us place a colonnette under each order, grouping them, either in the solid or as detached shafts, round a central square pier (Figs. 290, 291). In any of these methods we at once obtain the clustered column. [Illustration: Fig. 288.] [Illustration: Fig. 289.]