The emperors of the second century were almost all generals; they had the opportunity of waging numerous wars to repel the hostile peoples who sought to invade the empire. The enemies were in two quarters especially: 1. On the Danube were the Dacians, barbarous people, who occupied the country of mountains and forests now called Transylvania. 2. On the Euphrates was the great military monarchy of the Parthians which had its capital at Ctesiphon, near the ruins of Babylon, and which extended over all Persia. Trajan made several expeditions against the Dacians, crossed the Danube, won three great battles, and took the capital of the Dacians (101-102). He offered them peace, but when they reopened the war he resolved to end matters with them: he had a stone bridge built over the Danube, invaded Dacia and reduced it to a Roman province (106). Colonies were transferred thither, cities were built, and Dacia became a Roman province where Latin was spoken and Roman customs were assimilated. When the Roman armies withdrew at the end of the third century, the Latin language remained and continued throughout the Middle Ages, notwithstanding the invasions of the barbarian Slavs. It is from Transylvania (ancient Dacia) that the peoples came from the twelfth to the fourteenth century who now inhabit the plains to the north of the Danube. It has preserved the name of Rome (Roumania) and speaks a language derived from the Latin, like the French or Spanish. Trajan made war on the Parthians also. He crossed the Euphrates, took Ctesiphon, the capital, and advanced into Persia, even to Susa, whence he took away the massive gold throne of the kings of Persia. He constructed a fleet on the Tigris, descended the stream to its mouth and sailed into the Persian Gulf; he would have delighted, like Alexander, in the conquest of India. He took from the Parthians the country between the Euphrates and the Tigris--Assyria and Mesopotamia--and erected there two Roman provinces. 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.