me sectors from early in the second
century, and recruited, in increasing proportion, from among the children
of the camps, it only required the granting to them of frontier lands by
Severus Alexander, upon condition of their defending them, to complete
their transformation into a border militia (_limitanei_). At the same time
the scattering of the legions along the line of the frontiers made the
assembling of any adequate mobile force a matter of considerable time. And
the fortifications themselves, while useful in checking predatory raids by
isolated bands and in regulating intercourse across the frontiers, proved
incapable of preventing the invasion of larger forces. Consequently, when
in the third century the barbarians broke through the _limites_ they found
no forces capable of checking them until they had penetrated deeply into
the heart of the provinces.

The chaos which followed the death of Severus Alexander was the result of
a military policy which left the richest and most highly civilized parts
of the empire without any means of self-defence; created a huge
professional army the rank and file of which had come to lose all contact
with the ungarrisoned provinces, all interest in the maintenance of an
orderly government and all respect for civil authority; and at the same
time rendered the army itself incapable of performing the task for which
it was organized.

On the other hand the army had been one of the most influential agents in
the spread of the material and cultural aspects of Roman civilization. The
great highways of the empire, bridges, fortifications and numerous public
works of other sorts were constructed by the soldiers. Every camp was a
center for the spread of the Latin language and Roman institutions and the
number of Roman citizens was being augmented continuously by the stream of
discharged auxiliaries whose term of service had expired. In the
_canabae_, or villages of the civilian hangers-on of the army corps,
sprang up organized communities of Roman veterans with all the
institutions and material advantages of municipal life. The constant
movement of troops from one quarter of the empire to another furnished a
ready medium for the exchange of cultural, in particular of religious,
ideas. To the ideal of the empire the army remained loyal throughout the
principate, although this loyalty came at length to be interpreted in the
light of its own particular interests. Not only was the army the s