suddenness, the common--although not the universal--rule, that is
probably the outcome of the developments sketched in the last chapter.
Approximations to chess-board planning had been here and there
employed in the century before Alexander. When his conquests and their
complicated sequel led, amongst other results, to the foundation of
many new towns, it was natural that the most definite form of planning
should be chosen for general use.

We might, however, wonder whether its adoption was helped by the
military character of the generals who founded, and the discharged
soldiers who formed the first inhabitants of so many among these
towns. Military men are seldom averse to rigidity. It is worth noting,
in this connexion, that when chess-board planning came into common use
in the Roman Empire, many--perhaps most--of the towns to which it was
applied were 'coloniae' manned by time-expired soldiers. So, too, in
the Middle Ages and even in comparatively modern times, the towns laid
out with rectangular street-plans in northern Italy, in Provence, in
the Rhine Valley, are for the most part due in some way or other to
military needs.[23] In our own days rectangular planning is a dominant
feature of the largest and newest industrial towns. They are adapting
a military device to the purposes of an industrial age.

[23] Since the invention of artillery, the rectangular
street-plan has been regarded by soldiers as useful in defending
the streets of a town. Aristotle, however, expressly observes in
the _Politics_ that, in street warfare, tortuous lanes were far
better than straight avenues for the defence, and he recommends
that the rectangular pattern should be adopted only 'in parts and
in places', though he does not explain how this would work out
(_Politics,_ iv. 11, p. 1330).