t is
significant that the political boundary between them was here marked
by a little river, the Rubicon, a few miles to the north of that city.
The command which Rimini thus held was purely political; it passed
from her to Ravenna automatically whenever that entry was threatened.
Why?

The answer is very simple: because Rimini could not easily be
defended, while Ravenna was impregnable.

Ravenna stood from fifteen to eighteen miles north and east of the
Aemilian Way and some thirty-one miles north and a little west of
Rimini. Its extraordinary situation was almost unique in antiquity and
is only matched by one city of later times--Venice. It was built as
Venice is literally upon the waters. Strabo thus describes it:
"Situated in the marshes is the great Ravenna, built entirely on
piles, and traversed by canals which you cross by bridges or
ferry-boats. At the full tides it is washed by a considerable quantity
of sea water, as well as by the river, and thus the sewage is carried
off and the air purified; in fact, the district is considered so
salubrious that the (Roman) governors have selected it as a spot in
which to bring up and exercise the gladiators. It is a remarkable
peculiarity of this place that, though situated in the midst of a
marsh, the air is perfectly innocuous."[1]

[Footnote 1: Strabo, v. i. 7, tells us Altinum was similarly
situated.]

[Illustration: Sketch Map or Ravenna region in more detail]

Ravenna must always have been impregnable to any save a modern army,
so long as it was able to hold the road in and out and was not taken
from the sea. The one account we have of an attack upon it before the
fall of the empire is given us by Appian and recounts a raid from the
sea. It is but an incident in the civil wars of Marius and Sulla when
Ravenna, we learn, was occupied for the latter by Metellus his
lieutenant. In the year 82 B.C., says Appian, "Sulla overcame a
detachment of his enemies near Saturnia, and Metellus sailed round
toward Ravenna and took possession of the level wheat-growing country
of Uritanus."

This impregnable city, the most southern of Cisalpine Gaul,
immediately commanded the pass between Cisalpine Gaul and Italy
directly that pass was threatened, and to this I say was due a good
half of its fame. The rest must be equally divided between the fact
that the city was impregnable, and therefore a secure refuge or _point
d'appui_, and its situation upon the sea.

Strabo in his