| Konstantios Doukas | |
|---|---|
| Emperor of the Romans | |
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| Byzantine co-emperor | |
| Reign | 1060–1078 |
| Predecessor | Michael VII Doukas |
| Successor | Nikephoros III Botaneiates |
| Co-emperors | Leo Diogenes (1070–1071) Nikephoros Diogenes (1070–1071) Michael VII Doukas (1071–1078) Constantine Doukas (1074–1078) Andronikos Doukas (1068–1070s) |
| Born | 1060 |
| Died | 18 October 1081 Dyrrhachium |
| Dynasty | Doukas |
| Father | Constantine X Doukas |
| Mother | Eudokia Makrembolitissa |
Konstantios Doukas (Greek: Κωνστάντιος Δούκας, 1060 – 18 October 1081), Latinized as Constantius Ducas, was a junior Byzantine emperor from 1060 to 1078. Konstantios was the son of Emperor Constantine X Doukas and Empress Eudokia Makrembolitissa. Upon his birth, he was elevated to junior emperor, along with his brother Michael VII. He remained as junior emperor during the reigns of Constantine, Romanos IV, and Michael VII. He was handed over to Nikephoros III, a usurper, following the abdication of Michael VII. He was sent to live in a monastery, where he stayed until recalled by Alexios I Komnenos, who made him a general. He was killed in 1081, in the Battle of Dyrrhachium. Sources sometimes confuse him with his nephew, Constantine Doukas.