Isaac and Alexios Komnenos conducts a coup against Nikephoros III Botaneiates. Alexios and his forces broke through the walls of Constantinople on 1 April 1081 and sacked the city; Patriarch Cosmas convinced Nikephoros to abdicate to Alexios rather than prolong the civil war. Alexios becomes the new Byzantine Emperor.

At the very outset of his reign, Alexios was faced with multiple problems. He had to meet the formidable threat of the Normans under Robert Guiscard and his son Bohemond of Taranto. Also, taxation and the economy were in complete disarray. Inflation was spiralling out of control, the coinage was heavily debased, the fiscal system was confused (there were six different nomismata in circulation), and the imperial treasury was empty. In desperation, Alexios had been forced to finance his campaign against the Normans by using the wealth of the Eastern Orthodox Church, which had been put at his disposal by the Patriarch of Constantinople.