years earlier we have--what is more to our present purpose--a notice by
Ammianus Marcellinus of Saxons being leagued with the Picts and Scots,
and invading the territories south of the Forth, which were held by the
Romans and their conquered allies and dependants--the Britons.

To understand properly the remarks of Ammianus, it is necessary to
remember that the two great divisional military walls which the Romans
erected in Britain, stretched, as is well known, entirely across the
island--the most northerly from the Forth to the Clyde, and the second
and stronger from the Tyne to the Solway. The large tract of country
lying between these two military walls formed from time to time a
region, the possession of which seems to have been debated between the
Romans and the more northerly tribes; the Romans generally holding the
country up to the northern wall or beyond it, and occasionally being
apparently content with the southern wall as the boundary of their
empire.

About the year A.D. 369, the Roman general Theodosius, the father of the
future emperor of the same name, having collected a disciplined army in
the south, marched northward from London, and after a time conquered, or
rather reconquered, the debateable region between the two walls; erected
it into a fifth British province, which he named "Valentia," in honour
of Valens, the reigning emperor; and garrisoned and fortified the
borders (_limites_ que vigiliis tuebatur et praetenturis).[192] The
notices which the excellent contemporary historian, Ammianus
Marcellinus, has left us of the state of this part of Britain during the
ten years of active rebellion and war preceding this erection of the
province of Valentia are certainly very brief, but yet very interesting.
Under the year 360, he states that "In Britain, the stipulated peace
being broken, the incursions of the Scots and Picts, fierce nations,
laid waste the grounds lying next to the boundaries (loca _limitibus_
vicina vastarent)." "These grounds were," says Pinkerton, "surely those
of the future province of Valentia."[193] Four years subsequently, or in
364, Ammianus again alludes to the Britons being vexed by continued
attacks from the same tribes, namely the Picts and Scots, but he
describes these last as now assisted by, or leagued with, the Attacots
and with the _Saxons_--"Picti, SAXONESQUE, et Scotti, et Attacotti,
Britannos aerumnis vexavere continuis." Again, under the year 368, he
alludes to the