Neither its oblongs, nor its squares, nor its street-crossings exhibit true right angles, though many of the rooms and peristyles in the private houses are regular enough.

In this feature Pompeii resembles the trapezoidal outlines of the Terremare (fig.

11).

It resembles also much Roman military work, both of Republican and of Imperial date, which disregards the strict right angle and accepts squares and oblongs which are, so to say, askew.

The motive of the Terremare is supposed to have been, as I have said above, that of providing an easy flow for the water in the encircling moat.