Constans II, nicknamed "the Bearded", was emperor of the Byzantine Empire from 641 to 668. He was the last attested emperor to serve as consul, in 642, although the office continued to exist until the reign of Leo VI the Wise (r. 886–912).

Under Constans, the Byzantines completely withdrew from Egypt in 642. Constans attempted to steer a middle line in the church dispute between Orthodoxy and Monothelitism by refusing to persecute either and prohibiting further discussion of the natures of Jesus Christ by decree in 648 (the Type of Constans). In 654, however, Mu'awiya renewed his raids by sea, plundering Rhodes. Constans led a fleet to attack the Muslims at Phoinike (off Lycia) in 655 at the Battle of the Masts, but he was defeated: 500 Byzantine ships were destroyed in the battle, and the Emperor himself was almost killed.;In 658, with the eastern frontier under less pressure, Constans defeated the Slavs in the Balkans, temporarily reasserting some notion of Byzantine rule over them and resettled some of them in Anatolia (ca. 649 or 667). In 659 he campaigned far to the east, taking advantage of a rebellion against the Caliphate in Media. The same year he concluded peace with the Arabs. However, having attracted the hatred of the citizens of Constantinople, Constans decided to leave the capital and to move to Syracuse in Sicily.On his way, he stopped in Greece and fought the Slavs at Thessalonica with success. Then, in the winter of 662–663, he made his camp at Athens. From there, in 663, he continued to Italy. In 663 Constans visited Rome for twelve days—the only emperor to set foot in Rome for two centuries—and was received with great honor by Pope Vitalian (657–672).;