The regularity is not confined to single buildings, but extends to the relations of different edifices one to another.

The sides of buildings standing on one platform, at whatever distance they may be, are parallel.

There is, however, less consideration paid than we should have expected to the exact position, with respect to a main building, in which a subordinate one shall be placed.

Propylaea, for instance, are not opposite the centre of the edifice to which they conduct, but slightly on one side of the centre.

And generally, excepting in the parallelism of their sides, buildings seem placed with but slight regard to neighboring ones.
For effect, the Persian architecture must have depended, firstly, upon the harmony that is produced by the observance of regularity and proportion; and, secondly, upon two main features of the style.