He was married to an unnamed daughter of Isaac Angelos Doukas, uncle to the emperor Isaac II Angelos (r. 1185–1195, 1203–1204). Thus, Basil Vatatzes was married to a cousin of the emperor and was appointed by the latter as Domestic of the East and doux of the Thracesian Theme in Asia Minor.
Revolt of Theodore Mankaphas
Basil Vatatzes successfully suppressed the revolt of the usurper Theodore Mankaphas. The rebellion started circa 1188, when Theodore proclaimed himself as emperor in Philadelphia, Asia Minor, in opposition to Isaac II Angelos. After some initial skirmishes, in June 1189 Theodore was besieged in Philadelphia by imperial troops led by the emperor himself, who agreed to pardon Mankaphas as the latter submitted himself to Isaac and abandoned his aspirations to the throne. He was then allowed to retain control of Philadelphia as its governor.
In circa 1193 (or possibly 1190), however, in his capacity of doux of the Thracesian Theme and Domestic of the East (or perhaps as Grand Domestic of the Byzantine army), Basil Vatatzes was sent against Theodore Mankaphas, who had rebelled once more. This time Vataztes effectively ended the rebellion and forced the usurper to flee to the court of the Seljuk Turks at Iconium.
At some time before 1193 he was appointed Domestic of the West (as with his contemporary and co-commander, Alexios Gidos, it is unclear if he was Grand Domestic or simply Domestic), based at Adrianople. His primary task was to stop the incursions of the Bulgarians from the north of the Balkan mountains toward the European themes of the empire.
In 1193 he refused any military support to his brother-in-law Constantine Angelos Doukas, a cousin to the emperor and commander of the Byzantine armies in Philippopolis, when Doukas proclaimed himself emperor and marched his troops through Adrianople toward the capital Constantinople. Shortly before reaching Adrianople the usurper was betrayed by his followers and surrendered to Isaac II Angelos for a pardon in return.
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