Sasanian Persia

The Sasanians rebuilt the Persian empire and spent four centuries as Rome's only equal — the two powers fought, traded, and exhausted each other along the same frontier for longer than the United States has existed. They made Zoroastrianism a state religion, ran a sophisticated bureaucracy, and one of their kings captured a Roman emperor alive. Their final war with Byzantium in the 600s left both empires bankrupt and depleted, at precisely the moment armies came out of Arabia.