The city of Al-Hirah, widely known for its size and wealth, was a Sassanian dukedom as it was the capital of the Persian province of Iraq. Many of its Lakhmid Christian Arab inhabitants patrolled the desert on behalf of the Sassanians. According to the Roman historian, Procopius, the Lakhmids were "experienced at war, (and) completely loyal to the Persians (before 608 a.d., when the sassanids turned against them). During the reign of the Caliphate, Abu Bakr, sent Khalid ibn al-Walid a letter which noted that "The conquest of Al-Hirah and Kufa is entrusted to thee."