The city was a centre of Greek and Aramaic (Syriac) theological and philosophical thought, hosting the famed School of Edessa. Edessa remained in Roman hands until its capture by the Persians during the Byzantine–Sasanian War of 602–628, an event recorded by the Greek "Chronicon Paschale" as occurring in 609. Roman control was restored by the 627 and 628 victories of Heraclius () in the Byzantine–Sasanian War, but the city was lost to the Romans again in 638, to the Rashidun Caliphate during the Muslim conquest of the Levant. It did not return to the Romans' control until the Byzantine Empire temporarily recovered the city in the mid-10th century after a number of failed attempts.