With respect to the form of column other than its base and capital, it is in the first place round, circular-shaped, for it has to stand up in free and independent self-seclusion. The most essentially simple, securely exclusive, rationally defined[86], and most regular line is in fact the circle. For this reason the column already proves from its shape that it is not adapted to form an even surface when placed in adjacent rows, as is the case with adjacent posts which are squared to the rectangular corner, and so present walls and partitions, but it has merely the object to offer a support under its own self-limitation. Moreover the columnar structure is ordinarily reduced in size gradually, as it ascends from one-third of its height, it becomes less in circumference and thickness, because the portions beneath have to carry that above, and it is felt necessary to emphasize and make obvious also this mechanical relation of the several parts of the column itself. Finally, we frequently find that columns are grooved; the reason of this is twofold, first, essentially to diversify the simple form, and secondly to make the columns appear more thick by means of such a division where this is necessary.
(_γγ_) Although, then, the column is set up in independent isolation it has none the less to make it appear evident that it is not placed there for its own sake, but as subservient to the mass which it is erected to support. In so far as the house requires a boundary on every side the singular column is therefore not sufficient, but others have to be placed adjacent to it, in other words we come upon the definite conception of a diversity of columns placed in a _series._ And when several columns support the same weight this common service is at the same time that which determines the equal height which they all possess and which unites them together, in other words the beam. This marks the transition from the aspect of support to the opposed object supported.
(_β_) That which columns support is the _entablature_ superimposed. The relation of most importance to be considered here is that of _rectangularity._ Not merely in its relation to the ground, but also in that to the entablature the supporting structure must be rectangular. For the horizontal position is by the laws of gravity that which is alone intrinsically the most stable and fitting, and the right angle the only definitely secure one. The acute and obtuse angles are, on the contrary, indefinite, and both vary in their degree and are subject to contingency.