In December 633, the legendary Muslim warrior Khalid ibn al-Walid arrived at al-Firad, a fortress of one of the great powers of the day, the Sassanid Persian Empire. The other great power, the Byzantine Empire, seeing the Muslim advances all over Iraq, decided to aid the Persians against Khalid even though they had just fought a series of exhausting wars against each other.

The Ninth Century Muslim historian Tabari has the Persians and Byzantines exchanging intelligence about Khalid: “This is a man who is fighting on the basis of religion. He has intelligence and knowledge. By God, he will most definitely be victorious, whereas we will most certainly fail.” It is doubtful that Seventh Century Roman and Persian commanders were actually that defeatist, but they were certainly correct that Khalid was “fighting on the basis of religion.”

Everywhere he had gone in Persia, he had called the people to accept Islam or pay the jizya, the Qur’an-mandated tax for the “People of the Book.” For Khalid, the invasion of Persia was an expedition to bring Islam to the Sassanid Empire, or to subjugate the Zoroastrians and Christians in Persia under the rule of the Muslims. The Persians and Byzantines had every reason to be concerned. Khalid told his men: “Press your pursuit of them. Do not grant them any respite.” The Muslims won a decisive victory. Tabari notes that “the cavalry commander would corner a group of them with the spears of his men; having collected them, they would kill them.

On the day of al-Firad, one hundred thousand men were slain in the battle and the pursuit.” Around the same time, the Muslims were conquering the Holy Land. Sophronius, the patriarch of Jerusalem, in a sermon delivered in December 636 or 637, lamented the advent of “the Saracens” (he never referred to them as Muslims), “who, on account of our sins, have now risen up against us unexpectedly and ravage all with cruel and feral design, with impious and godless audacity.”