The next emperor who merits attention is Heraclius (610), a native of Africa. The Eastern Empire had till now preserved its ancient boundaries in their full extent, and was mistress of Carthage, Egypt, Syria, and Asia Minor, besides Greece, and the countries on the Danube. The Roman armies on the eastern frontier had, however, been lately driven in by Chosroes, king of Persia, who now occupied all the north of Africa and Syria. This was the first great violation of their territory sustained by the emperors of Constantinople; and Heraclius avenged it with a celerity and effect which made the Persians tremble. His triumph, however, was short, for the latter part of his reign was disturbed by the rise and victories of Mohammed. The successors of this signal impostor, after breaking the power of Persia (already weakened by the victories of Heraclius), immediately attacked the Roman Empire; then defeated its armies in two battles, occupied all Syria, and obliged the emperor (now an old man) to retire to Constantinople. He died in 641. The continued victories of the followers of Mohammed (called Arabs or Saracens) soon deprived the Empire of Egypt, Africa, and Syria; and in 668 they followed up their success by attacking Constantinople itself. The city sustained two sieges, in the first of which the Saracens were encamped in its neighborhood, and carried on the operations of a siege at intervals, for seven years; and in the second, for nearly two. In both the Saracens wasted immense resources ineffectually.