an eminent Byzantine philosopher and ecclesiastic of the 9th century, characterized by his devotion to learning, studied grammar and poetry at Constantinople, and rhetoric, philosophy, and arithmetic under Michael Psellus on the island of Andros, and at the monasteries on the adjacent part of continental Greece. He afterwards settled at Constantinople and became an instructor. Introduced to the notice of emperor Theophilus, he was appointed public teacher or professor, and the Church of the Forty Miartyrs was assigned him for a school. Soon after the patriarch John, who appears hitherto to have neglected his learned kinsman, promoted Leo to the archbishopric of Thessalonica. Upon the death of Theophilus (A.D. 842), when the government came into the hands of Theodora, the iconoclastic party was overthrown, and Leo and John were deposed from their sees; but Leo, whose worth seems to have secured respect, escaped the sufferings which fell to his kinsman's lot; and when Caesar Bardas, anxious for the revival of learning, established the mathematical school at the palace of Magnaura, in Constantinople, Leo was placed at the head.
Leo was still living in A.D. 869: how much later is not known. Symeon (De Mich. et Theodora, c. 46) has described a remarkable method of telegraphic communication invented by Leo, and practiced in the reigns of Theophilus and his son Michael. Fires kindled at certain hours of the day conveyed intelligence of hostile incursions, battles, conflagrations, and the other incilents of war, from the confines of Syria to Constantinople; the hour of kindling indicating the nature of the accident, according to an arranged plan, marked on the dial-plate of a clock kept in the castle of Lusus, near Tarsus, and of a corresponding one kept in the palace at Constantinople. The Μέθοδος προγνοστική , Methodus Prognostica, or instructions for divining by the Gospel or Psalter, by Leo Sapiens, in the Medicean Library at Florence (Bandini, Catalog. Codd. Laurn. Medic. 3:339), is perhaps by another Leo. Combefis was disposed to claim for Leo of Thessalonica the authorship of the celebrated Χρησμοί, Oracula, which are commonly ascribed to the emperor Leo VI, Sapiens, or the Wise, and have been repeatedly published. But Leo of Thessalonica is generally designated in the Byzantine writers the philosopher (φιλάσοφος ), not the wise (σοφός ); and if the published Oracula are a part of the series mentioned by Zonaras (15:21), they must be older than either the emperor or Leo of Thessalonica. See Fabricius, Bibl. Graeca, 4:148, 158; 7:697; 11:665; Allatius, De Psellis, 100:3-6; Labbe, De Byzant. Histor. Scriptoribus Προτρεπτικόν, pt. 2, p. 45. — Smith, Dict. of Grk. and Roman Biog. 2:745 sq.