Leo VI, byname Leo The Wise, or The Philosopher, (born Sept. 19, 866—died May 11, 912, Constantinople), Byzantine coemperor from 870 and emperor from 886 to 912, whose imperial laws, written in Greek, became the legal code of the Byzantine Empire.
Leo was the son of Basil I the Macedonian, who had begun the codification, and his second wife, Eudocia Ingerina. Made coemperor in 870, Leo succeeded to the throne on his father’s death. His foreign policy was directed mainly against the Arabs and the Bulgars. The able commander Nicephorus Phocas the Elder was recalled from his successful campaigns against the Lombards in south Italy to assist in the Balkans. After this Byzantium met with reverses in the West: Sicily was lost to the Arabs in 902, Thessalonica was sacked by Leo of Tripoli, and the Aegean was open to constant attack from Arab pirates. Steps were taken to strengthen the Byzantine navy, which successfully attacked the Arab fleet in the Aegean in 908. But the naval expedition of 911–912 was defeated by Leo of Tripoli. Byzantium’s enemy to the north was Simeon, the Bulgar ruler. Hostilities arose out of a trade dispute in 894, and the Byzantines, aided by the Magyars of the Danube-Dnieper region, forced Simeon to agree to a truce. With the help of the nomadic Pechenegs, however, Simeon in 896 took revenge on the Byzantines, forcing them to pay an annual tribute to the Bulgars.
During Leo’s reign the Russian prince Oleg sailed to Constantinople and in 907 obtained a treaty regulating the position of Russian merchants in Byzantium, which was formally ratified in 911. Because of his anxiety for a male heir Leo married four times, thus incurring the censure of the church.
Educated by the patriarch Photius, Leo was more scholar than soldier. In addition to completing the canon of laws, he wrote several decrees (novels) on a wide range of ecclesiastical and secular problems. He also wrote a funeral panegyric on his father, liturgical poems, sermons and orations, secular poetry, and military treatises. Leo’s image is in a mosaic over the central door of Hagia Sophia.