To commemorate his conquests Trajan erected monuments which still remain.  The Column of Trajan on the Roman Forum is a shaft whose bas-reliefs represent the war against the Dacians.  The arch of triumph of Benevento recalls the victories over the Parthians.

Of these two conquests one alone was permanent, that of Dacia.  The provinces conquered from the Parthians revolted after the departure of the Roman army.  The emperor Hadrian retained Dacia, but returned their provinces to the Parthians, and the Roman empire again made the Euphrates its eastern frontier.  To escape further warfare with the highlanders of Scotland, Hadrian built a wall in the north of England (the Wall of Hadrian) extending across the whole island.  There was no need of other wars save against the revolting Jews; these people were overthrown and expelled from Jerusalem, the name of which was changed to obliterate the memory of the old Jewish kingdom.

Marcus Aurelius, the last of the Antonines, had to resist the invasion of several barbarous peoples of Germany who had crossed the Danube on the ice and had penetrated even to Aquileia, in the north of Italy.  In order to enroll a sufficient army he had to enlist slaves and barbarians (172).  The Germans retreated, but while Marcus was occupied with a general uprising in Syria, they renewed their attacks on the empire, and the emperor died on the banks of the Danube (180).  This was the end of conquest.

IMPERIAL ADMINISTRATION

=Extent of the Empire in the Second Century.=—­The Roman emperors were but little bent on conquest.  But to occupy their army and to secure frontiers which might be easily defended, they continued to conquer barbarian peoples for more than a century.  When the course of conquest was finally arrested after Trajan, the empire extended over all the south of Europe, all the north of Africa and the west of Asia; it was limited only by natural frontiers—­the ocean to the west; the mountains of Scotland, the Rhine, the Danube, and the Caucasus to the north; the deserts of the Euphrates and of Arabia to the east; the cataracts of the Nile and the great desert to the south.  The empire, therefore, embraced the countries which now constitute England, Spain, Italy, France, Belgium, Switzerland, Bavaria, Austria, Hungary, European Turkey, Morocco, Algiers, Tunis, Egypt, Syria, Palestine, and Asiatic Turkey.  It was more than double the extent of the empire of Alexander.

This immense territory was subdivided into forty-eight provinces,[147] unequal in size, but the majority of them very large.  Thus Gaul from the Pyrenees to the Rhine formed but seven provinces.