and Syria between them, and the boundaries shifted east and west as either side grew stronger. We have marked the utmost eastward extension of the Roman Empire under Trajan (see map to chap. xxix., § 3), and we have noted that about the same time the Indo-Scythians (chap. xxix., § 4), poured down into India.
In 227 occurred a revolution, and the Arsacid dynasty gave way to a more vigorous line, the Sassanid, a national Persian line under Ardashir I. In one respect the empire of Ardashir I presented a curious parallelism with that of Constantine the Great a hundred years later. Ardashir attempted to consolidate it by insisting upon religious unity, and adopted as the state religion the old Persian faith of Zoroaster, of which we shall have more to say later.
This new Sassanid Empire immediately became aggressive, and under Sapor I, the son and successor of Ardashir, took Antioch. We have already noted how the Emperor Valerian was defeated (260) and taken prisoner. But as Sapor was retiring from a victorious march into Asia Minor, he was fallen upon and defeated by Odenathus, the Arab king of a great desert-trading centre, Palmyra.
For a brief time under Odenathus, and then under his widow Zenobia, Palmyra was a considerable state, wedged between the two empires. Then it fell to the Emperor Aurelian, who carried off Zenobia in chains to grace his triumph at Rome (272).
We will not attempt to trace the fluctuating fortunes of the Sassanids during the next three centuries. Throughout that time war between Persia and the empire of Constantinople wasted Asia Minor like a fever. Christianity spread widely and was persecuted, for after the Christianization of Rome the Persian monarch remained the only god-monarch on earth, and he saw in Christianity merely the propaganda of his Byzantine rival. Constantinople became the protector of the Christians and Persia of the Zoroastrians; in a treaty of 422, the one empire agreed to tolerate Zoroastrianism and the other Christianity. In 483, the Christians of the east split off from the Orthodox church and became the Nestorian church; which, as we have already noted, spread its missionaries far and wide throughout Central and Eastern Asia. This separation from Europe, since it freed the
