It does not follow, when we find streets in the ruins of an ancient city, that they must belong to its earliest period.

That is not true of towns in any age, modern or mediaeval, Roman or Greek.

Some Greek cities were founded in early times, were rebuilt in the Macedonian period, and again rebuilt in the Roman period.

Without minute excavation it may be impossible to assign the town-plan of such a place to its proper place among these three periods.
We have, however, at Selinus in Sicily and Cyrene on the north coast of Africa, two cases which may belong to the age of Hippodamus.

They are worth describing, since they illustrate both the difficulty of reaching quite certain conclusions and also the system which probably did obtain in the later fifth and the early fourth century.
_Selinus_ (fig.