Constantine Mesopotamites () was a senior Byzantine official, and de facto chief minister under the emperors Isaac II Angelos and Alexios III Angelos from 1193 until his fall in summer 1197. He was also archbishop of Thessalonica from until , but was in exile between 1204 and 1224, when the city was occupied by Latin Crusaders. Restored to his see, he refused to crown Theodore Komnenos Doukas as emperor, and departed his see again in self-exile. He was also a colleague and correspondent of the historian Niketas Choniates, and may have commissioned some of the latter's works.
Life
Constantine's family, the Mesopotamitai, appeared in the late 11th century, and originated either from Mesopotamos (in modern Albania) or some place called Mesopotamia. One of his early assignments in the public service was as ambassador to the Republic of Genoa in , to negotiate a treaty. When Mesopotamites returned with his Genoese counterpart, Simone Bufferio, to Constantinople in order to ratify the treaty, however, it was discovered that he had overstepped his brief, leading to a temporary collapse in negotiations.
Career under Isaac II
In 1193, despite his extreme youth—his colleague and historian Niketas Choniates refers to him derisively as a "small boy [...] less than a year after he had put down pen and ink [i.e. left school]"—he was chosen by Emperor Isaac II Angelos () to succeed his maternal uncle and chief minister, Theodore Kastamonites, when the latter suffered a stroke and died soon after. Holding the rank of epi tou kanikleiou (keeper of the imperial inkstand), he quickly succeeded in placing Isaac entirely under his influence. According to Choniates he exercised power greater than that even of his predecessor, while historian Charles Brand credits him with "combining craft and guile with real ability in the management of affairs". During this period, Mesopotamites was also the recipient of a eulogy by Nikephoros Chrysoberges.
Mesopotamites' hold over the administration was secured by effectively isolating the emperor from public affairs, including ending Isaac's predilection for personally leading campaigns. Like Kastamonites, he was particularly successful in excluding the court and the nobility from power. As a result, he was greatly hated by the aristocracy, who plotted against Isaac. In the event, this resentment found an outlet in Isaac's elder brother, Alexios III Angelos (r. 1195–1203), who in April 1195 with the support of the aristocracy seized the throne while Isaac was hunting. Isaac was captured and blinded, being confined thereafter in a palace near the Golden Horn.
Career under Alexios III
Among the first acts of the new emperor was the dismissal of Mesopotamites, but as the new regime quickly degenerated into a wholesale plundering of the state coffers and the open sale of offices, Empress Euphrosyne Doukaina Kamatera intervened with her husband and secured his reinstatement, probably in late 1195. Returning to his old office of epi tou kanikleiou, Mesopotamites soon enjoyed as dominant a position under Alexios as he had under Isaac: the aristocratic courtiers, including the emperor's son-in-law Andronikos Kontostephanos and the empress' brother Basil Kamateros, lost power, while Mesopotamites became in Alexios' eyes "the horn of plenty, the mixing-bowl of virtues". Choniates' account suggests that he was indeed successful in improving administration during his renewed ascendancy.
Unable to attack him directly, in summer 1196 Kamateros and Kontostephanos accused the empress of infidelity with a certain Vatatzes, an adopted son of Alexios III. The emperor ordered Vatatzes executed, and two months later the empress was banished to a monastery at Nematarea. Her exile proved unpopular with the populace, and her relatives and supporters, Mesopotamites foremost, secured her pardon after six months, in March 1197. She quickly restored her influence over her husband, and alongside her Mesopotamites now stood at the summit of his power. According to Choniates, Mesopotamites now considered the title of epi tou kanikleiou insufficient, and sought to be elevated from the ecclesiastical rank of lector to deacon. This was granted, with Patriarch George Xiphilinos himself performing the ceremony. In addition, Mesopotamites was granted precedence among all other deacons, and a special dispensation was given for Mesopotamites to continue serving in the civil administration, as this was not normally allowed to ecclesiastics.