Complex sentence: In 721, Anastasius headed a revolt against Leo, who had succeeded Theodosius, and receiving a considerable amount of support, laid siege to Constantinople; but the enterprise failed, and Anastasius, falling into Leo's hands, was put to death by his orders.
Split into simpler sentences: In 721, Anastasius headed a revolt against Leo, who had succeeded Theodosius, and receiving a considerable amount of support, laid siege to Constantinople. The enterprise failed, and Anastasius, falling into Leo's hands, was put to death by his orders.