Mauros, who was called that on account of his extremely black beard, was a patrician in Constantinople during the second part of the reign of Justinian II. The emperor first encountered Mauros when the patrician told him of his suspicion of Leo, a young officer whom he suspected of plotting against Justinian though he had no evidence. Mauros was the second such person to talk to Justinian about Leo. Combined with the accusations provided by Helias and by Stephen, who followed Mauros some two weeks later, and despite the fact that none of them had any evidence to back up their accusations, Justinian investigated the matter and realized Leo had several mistresses scattered throughout Constantinople in addition to his wife. Deciding that hiding the existence of the mistresses from his wife was the sign of a deceptive mentality that could easily work against him, Justinian packed Leo off on a military mission to eastern Anatolia.
When the expedition to destroy the city of Kherson was launched, some years later, Mauros was one of the men selected to lead it, along with Helias, Stephen, and Bardanes. Justinian gave Mauros, Helias and Stephen their bloodthirsty orders to raze and slaughter the inhabitants, and an additional order to observe Bardanes and make sure he did his job competently (which translated to leave no survivors) and obediently. They put many Khersonites to the sword; others they drowned with elaborate detail in the Black Sea. But the inability to slaughter young children infuriated Justinian and drove him to order the three leaders back to the capital and almost certain execution. Mauros heeded the call, and kept his health; Stephen, Bardanes and Helias remained in Kherson, and became enemies of state.
After a second expedition to finish the Kherson job had failed, Justinian sent Mauros on a third trip with a very clear warning instructing him what he and his relatives could expect should he fail. Mauros' army managed to break down a gate, but then the army of Ibouzeros Gliabanos descended on the siege and checked Mauros; Mauros realized he was too weak to take the town, and he also couldn't face Justinian again, so he declared for the rebels. Bardanes marched on Constantinople and took the city; Mauros found Justinian's son Tiberius hiding in a church. When Anastasia, mother of Justinian, objected to the murder of one so little, Mauros reminded her that Helias' children, murdered upon word of Helias' treason, were just as little, and accompanied John the Ostrich into the church to do the job.