A MEDITERRANEAN EMPIRE 21as far north as southern Scotland and the Rhine and Danube (with the
addition of a slice of southern Germany across the Rhine and Dacia across
the central Danube). The most extensive advances under the Principate were
made in Europe during the rule of the fi rst emperor, Augustus. His generals
pushed the northern frontier from the Alps to the Danube and fi nally pacifi ed
the Iberian peninsula.^5
Augustus achieved much less than he intended. He appears to have
nurtured the grandiose ambition of advancing beyond the Rhine to the
China sea, that is, to the ocean in the East. A map of the world begun by his
right- hand man Agrippa, completed under the direction of the emperor and
displayed by him on a portico in Rome, showed this distance to be no more
than three and a half times the breadth of Gaul, east to west.^6 An expedition
to China over the Elbe, if it had ever been launched, would probably have
been even more of a shambles than that of Augustus’ prefect of Egypt, Aelius
Gallus, into Arabia, since they shared a profound ignorance of geography
(Strabo 780–2; Pliny, HN 6.159–62). As it was, the military effort was
stalled between the Rhine and Elbe; the Germans, formidable opponents in
any case, were able to exploit Roman ignorance of the terrain.
Beyond the motive of sheer conquest, strategic and sometimes economic
considerations played some part in shaping the campaigns of militarily
active emperors.^7 In the case of Augustus these motives help to explain, on
the one hand, the conquest of the previously untamed Cantabrian and
Asturian tribes of the interior of the Iberian peninsula, with the object of
tapping the mineral resources of the mountains and enhancing the security
of the coastal plains and river valleys; and, on the other hand, the absence
of a campaign in Britain, thought to be poor in resources and no great threat
to Gaul (Strabo 115–16). The annexation of Britain in AD 43 was a distraction
from the political embarrassments of Claudius’ accession and early years; it
was not that wise men in Rome had revised their view of the value of the
country. The conviction that Britain was not worth anything to Rome
lingered on (Appian, BC pref. 5).
Elsewhere, the eastern frontier was the main theatre of war. Persia
exercised a fatal attraction for the more militarily ambitious emperors, as it
had done for a succession of would- be emulators of Alexander the Great in
the closing decades of the Republic, most notably Crassus, Caesar and
Antony. Trajan ( AD 96–117) followed up his two Dacian wars and eventual
annexation of Dacia with a vigorous campaign east of the Euphrates, which
led to the establishment, briefl y, of the provinces of Armenia, Parthia and
Assyria (Adiabene, beyond the Tigris). His motive, according to the historian
Cassius Dio (68.17.1), was a desire for glory. The expedition of Lucius Verus
in AD 167 deep into Parthian territory was punitive rather than annexationist,
but Septimius Severus established the provinces of Mesopotamia and
Osrhoene beyond the Euphrates in the late 190s. Cassius Dio, a contemporary,
was not convinced of the permanence of these conquests: ‘Severus... was in
the habit of saying that he had gained a large additional territory and made