al inference is that Hadrian built his wall of [v.04 p.0586] turf and
Severus reconstructed it in stone. The reconstruction probably followed in
general the line of Hadrian's wall in order to utilize the existing ditch,
and this explains why the turf wall itself survives only at special points.
In general it was destroyed to make way for the new wall in stone.
Occasionally (as at Birdoswald) there was a deviation, and the older work
survived. This conversion of earthwork into stone in the age of Severus can
be paralleled from other parts of the Roman empire.

[Illustration: FIG. 3.--Section of Hadrian's Wall.]

The meaning of the _vallum_ is much more doubtful. John Hodgson and Bruce,
the local authorities of the 19th century, supposed that it was erected to
defend the wall from southern insurgents. Others have ascribed it to
Agricola, or have thought it to be the wall of Hadrian, or even assigned it
to pre-Roman natives. The two facts that are clear about it are, that it is
a Roman work, no older than Hadrian (if so old), and that it was not
intended, like the wall, for military defence. Probably it is
contemporaneous with either the turf wall or the stone wall, and marked
some limit of the civil province of Britain. Beyond this we cannot at
present go.

III. _The Civilization of Roman Britain._--Behind these formidable
garrisons, sheltered from barbarians and in easy contact with the Roman
empire, stretched the lowlands of southern and eastern Britain. Here a
civilized life grew up, and Roman culture spread. This part of Britain
became Romanized. In the lands looking on to the Thames estuary (Kent,
Essex, Middlesex) the process had perhaps begun before the Roman conquest.
It was continued after that event, and in two ways. To some extent it was
definitely encouraged by the Roman government, which here, as elsewhere,
founded towns peopled with Roman citizens--generally discharged
legionaries--and endowed them with franchise and constitution like those of
the Italian municipalities. It developed still more by its own automatic
growth. The coherent civilization of the Romans was accepted by the
Britons, as it was by the Gauls, with something like enthusiasm. Encouraged
perhaps by sympathetic Romans, spurred on still more by their own
instincts, and led no doubt by their nobles, they began to speak Latin, to
use the material resources of Roman civilized life, and in time to consider
themselves not the unwilling subjects