"Say to the desert Arabs who lagged behind: 'You shall be summoned against a people given to vehement war: you shall fight them, or they shall submit.
Then if you show obedience, Allah will grant you a goodly reward, but if you turn back as you did before, He will punish you with a painful Punishment."
The fort of Nujair, the last stronghold of apostasy, had fallen to the Muslims in about the middle of February 633. Soon after, Abu Bakr wrote to Khalid, who was still at Yamamah: "Proceed to Iraq. Start operations in the region of Uballa. Fight the Persians and the people who inhabit their land. Your objective is Hira."1
It was a big order. Abu Bakr was taking on the mightiest empire of the time, before which the world had trembled for more than a thousand years.
The Persian Empire was unique in many ways. It was the first truly great empire of history, stretching, in the time of the early Achaemenians, from Northern Greece in the west to the Punjab in the east. It was unique also in the length of time over which it flourished-from the Sixth Century BC to the Seventh Century AD, except for a gap caused by the Greek conquest.2 No other empire in history had lasted so long in all its greatness as a force of culture and civilisation and as a military power. It had known reverses, but after each reverse it had risen again in its characteristic glory and brilliance.
The last golden age of Persia had occurred in the Sixth Century AD when Anushirwan the Just restored the empire to its earlier level of greatness. Anushirwan reigned for 48 years and was a contemporary of Justinian. He wrested Syria from the Romans, the Yemen from the Abyssinians, and much of Central Asia from the Turks and other wild tribes of the steppes. This magnificent emperor died in 579, nine years after the birth of Prophet Muhammad.
As often happens when a great ruler passes away, Anushirwan was followed by a number of lesser mortals and the glory and prosperity of the empire began to fade. Civil war and intrigue sapped the strength of the state. The decline approached its climax in the time of Shiruya (Ciroes) a great-grandson of Anushirwan, who first imprisoned and then killed his father, Chosroes Parwez. Not content with this heinous crime, he turned to worse cruelties. So that none may dispute his right to the throne or pose a challenge to his authority, he had all the male members of his family killed with the exception of his son, Ardshir. The estimate of those of the house of Anushirwan who lost their lives to the maniacal fury of Shiruya, adult and child, varies from 15 to 18. And Shiruya reigned for only seven months before he too was dead.
With his death the confusion became worse. And there is confusion also in the accounts of the early historians about the order in which various emperors followed Shiruya and the duration of their respective reigns. All that is certain and unanimously accepted is the position of Yazdjurd bin Shahryar bin Perwez, who somehow escaped the assassins of Shiruya and became the last Persian Emperor of the line of Sasan. This ill-starred young man was to see the final disintegration of the great empire of the Chosroes.
1. Tabari: Vol. 2, pp. 553-4.
2. The Parthians, who overthrew the Seleucid power, though not Persians, were nevertheless Iranians. Thus the Greek interlude lasted less than two centuries until its end at the hands of the Parthians in the middle of the Second Century BC, The Persian Sasanids came to power in 220 AD.