administrative decay by the middle of the fourth century. Christianity
perhaps was already undermining the servile state, which in its effort
of self-preservation adopted an economic system hopelessly at variance
with the facts of the situation; while the weakness of its frontiers
offered a military problem which the empire was unable to face.
Diocletian had attempted to solve it by dividing the empire, but the
division he made was rather racial that strategic, for under it the
two parts of the empire, East and West, met on the Danube. The eastern
part, by force of geography, was inclined to an Asiatic point of view
and to the neglect of the Danube; the western was by no means strong
enough either financially or militarily to hold that tremendous line.

We read, in the letters of S. Ambrose among others, of the decay of
the great cities of Cisalpine Gaul,[1] of the failure of agriculture
in that rich countryside, of the poverty and misery that were
everywhere falling upon that great state. It is possible that in the
general weakening of administrative power even the roads, the canals,
the whole system of communications were allowed to become less perfect
than they had been; everywhere there was a retreat. The frontiers were
no longer inviolate, and it is probable that in the general decay the
port of Classis, the city of Ravenna, suffered not less than their
neighbours.

[Footnote 1: See S. Ambrose, _Ep_. 39, written in 388, quoted by
Muratori, _Dissertazioni_, vol. i. 21. "De Bonomensi veniens Urbe, a
tergo Claternam, ipsam Bononiam, Mutinam, Regium derelinquebas; in
dextera erat Brixillum; a fronte occurrebat Placentia.... Te igitur
semirutarum Urbium cadavera, terrarumque sub eodem conspectu exposita
funera non te admonent...."]