emperor of Constantinople (A. D. 813-820), succeeded Michael I. Rhangabe, on the 11th of July, 813: he was of noble Armenian descent, and the son of the celebrated Bardas Patricius. Leo enjoyed great renown as a skilful and intrepid general, and was highly esteemed by the emperor Nicephorus I. (802-811), whom he rewarded, however, with treachery. He was punished with exile, from which he was recalled in 811 by his friend Michael I., who succeeded Nicephorus in that year. Michael appointed him dux Orientis, and was served in the same way as his predecessor. The wife of Michael, Procopia, having obtained great influence over her husband, was the cause of a wide-spread disaffection of the army, and Leo availed himself of this circumstance to seize the crown. There is a story of an old woman at Constantinople, a prophetess, who predicted the speedy downfall of Michael and the elevation of Leo, who seems to have turned the superstition of the Greeks to his own advantage. While Leo carried on a successful war against the Arabs in Asia, the emperor fought with great disadvantage against Crum, king of the Bulgarians, who in 812 took Mesembrya, and threatened Constantinople. His defeats obliged Michael to recall Leo from Asia, and in the spring of 813 the emperor and Leo set out from Constantinople, at the head of one of the finest and most numerous armies that the Greeks had ever seen. Michael intended to harass the Bulgarians by manoeuvres, avoiding any decisive conflict. His wise delay was secretly approved of by Leo and his confederates, but they persuaded the army that the emperor was a coward, who followed the advice of his wife rather than that of his generals, and the poor emperor was forsaken before he had any idea how and by whom. The Greeks met the Bulgarians in the environs of Adrianople; but Michael, seeing the strong position of the enemy, declined again to risk a pitched battle. Now Leo and his friends urged him with all their might to attack Crum; and the Greek soldiers showed such violent anger at being again disappointed in coming to close quarters with the barbarians, that on the 22d of June the emperor gave orders for the attack. The conflict took a favourable turn for the Greeks, and every body prognosticated a complete victory, when Leo, with his Cappadocians and Armenians, suddenly took to flight, and caused a total rout of the imperial army. Michael saved himself within the walls of Adrianople, and in the evening Leo arrived with his troops. Nobody ventured to acquaint the emperor with the real cause of Leo's flight; and the remnants of the army being too much disorganised to risk a second battle, he followed the council of the treacherous general, and withdrew to Constantinople. There Joannes Hexabulus, the honest governor of the capital, mentioned to him his suspicions of Leo, but met with disbelief, till Leo appeared with his troops under the walls of Constantinople, and made his entrance into the city, without meeting with any opposition. After the departure of Michael from Adrianople, the friends of Leo induced the soldiers to proclaim as emperor the gallant Armenian, instead of the coward who was still their master; but Leo refused to accept the crown till, with feigned indignation, his friend and subsequent successor, Michael the Stammerer, rushed upon him with his drawn sword, crying with the accents of rage, " With this sword I will open the gates of Constantinople, or plunge it into thy heart, if thou refusest any longer to comply with the just wishes of thy comrades." Upon this Leo threw off the mask, marched upon Constantinople, and seated himself on the throne, from which Michael descended without murmuring, and retired into a convent, where he lived during upwards of thirty years.

No sooner was Leo crowned than Crum appeared before Constantinople. IIe burnt its suburbs, with all its magnificent buildings, withdrew to take Adrianople, and send its inhabitants into slavery, appeared again near the capital, and continued his devastations till Thrace was a desert. Having no army, Leo showed the greatest activity in forming one, and his efforts were already crowned with success, when Crum suddenly died in one of the gardens of Constantinople (814), and was succeeded by king Deucom. Now Leo sallied out. At Mesembrya he brought the Bulgarians to a stand, and took bloody revenge for the calamities they had brought upon Greece: the barbarian army was annihilated. In 815 Deucom appeared again, and met with a similar fate, whereupon Leo invaded Bulgaria, defeated the barbarians wherever he met them, and ravaged the country in a manner still worse than the Bulgarians had done in Thrace. Such was the consternation of the barbarians, that Mortagon, the successor of Deucom, deemed himself fortunate in obtaining a peace for thirty years; and such was the impression made upon the minds of his unruly subjects by the fierce onsets of Leo, that they remained quiet during seventy-four years. Thus Leo crushed the hereditary and most dangerous enemy of the Byzantine empire.

The empire now enjoyed peace, and Leo was active in restoring the happiness of his subjects. He protected the Iconoclasts, and showed himself a firm, though often cruel, opponent of the worshippers of images; hence arose many conspiracies, which he quelled with ease. He reformed the whole system of administration. Before his reign all the civil and military offices were sold to the highest bidder; he, on the contrary, gave them to the worthiest, and punished severely all those that were found guilty of peculation. He often presided in the courts of justice; and woe to those judges who had acted unfairly or unjustly. In his punishments, however, he observed no just proportion; decapitation, mutilation, or banishment, being as often inflicted for slight offences as for capital crimes. Pleasure was unknown to him, but that which arises from the satisfaction of having done one's duty. Day and night he was at work. Most of the provinces he visited, and his occasional visits had a still more beneficial effect, since he always arrived without being announced. His conduct towards the adorers of images, however, created him many enemies; and at last his best friend became the cause of his ruin. Michael the Stammerer, though a staunch adherent of Leo, could not help blaming him for many actions; and being no master of his sharp tongue, his words produced more effect than he intended. This annoyed Leo, who ordered Michael to inspect the troops in Asia, as the best means of getting rid of him at court. Michael refused to comply with the order, and was soon surrounded by a crowd of the secret enemies of Leo, who persuaded him to enter into their plans. The honest Hexabulus was informed of the plot, and Michael was seized, tried, and sentenced to be burnt alive in a furnace It was just Christmas eve 820, and he was to be executed on the same day. Leo left his palace to witness the execution, and the unhappy man, loaded with chains, was dragged along, when the empress besought her husband not to carry out his bloody verdict on that sacred day, but to wait till after Christmas. Leo, moved by her entreaties, ordered Michael to be taken back to his prison. On the following day the emperor and his whole court went in procession to church, and according to a custom established at the Byzantine court, the emperor himself began the sacred chant. This was the signal of his death. During the night the friends of Michael had resolved to risk every thing in order to save his and their own lives; and dressed in the garb of priests, with arms hid under their floating garments, they entered the church without creating any suspicion. At the moment they heard Leo's voice they rushed upon him. He escaped to the altar, and defended himself with the great cross; but in vain-nobody came to his rescue. Exhausted by an heroic resistance, he saw one of his murderers, of gigantic stature, aim a fatal blow at him. " Have mercy ! " cried the fainting emperor. "This is not the hour of mercy," replied the giant, "but the hour of revenge! " and with one blow he felled him to the ground. Michael was now dragged from his prison, and, as Gibbon says, he was snatched from the fiery furnace to the sovereignty of an empire. Leo left four sons, the eldest of whom, Sarbatius or Symbatius, was crowned as his father's future successor shortly after the deposition of Michael Rhangabe. They were all castrated by order of Michael the Stammerer, and confined in a convent. Sarbatius died in consequence of the operation. (Theoph. p. 424, &c.; Theoph. Contin. p. 428, &c.; Cedren. p. 483, &c.; Zonar. vol. ii. p. 127, &c.; Leo Gram. p. 445, &c.; Const. Manass. p. 94; Joel, p. 287; Glycas, p. 287, &c.; Genesius, p. 2, &c.)