By the mid-620s, the Persian king Khusro II had conquered most of the Eastern Roman Empire. A final push toward Constantinople was planned. The armies of Iran and her nomadic allies of the steppe were to descend upon the capital, blockade it by land and sea, and receive the emperor’s surrender. The nobles and retired worthies of the Roman Senate had earlier sent a grovelling letter to the Persian government, urging Khusro to impose a client king over them and spare what was left of the empire. But Khusro ignored it. For a moment, the extinction of 800 years of Roman rule in the Mediterranean world hung in the balance. Khusro’s authority now stretched from the Nile to the Euphrates and from the Tigris to the Indus, and was about to be extended into Europe. Like his Persian forebears Cyrus and Darius, he commissioned monumental rock reliefs to commemorate his conquests. His vast empire might have lasted for centuries, binding together the fringes of Europe with North Africa and the Levant with the Iranian plateau, …