it probable that Bulgarians, Vlachs and Cumans were among their ancestors. Robert of Clari, author of a chronicle of the early history of the Latin Empire of Constantinople, stated that Asen (whom Clari confused with his younger brother, Kaloyan) had "once [been] a sergeant of the emperor, having charge of one of the emperor's horse farms". He noted that Asen was obliged to send sixty to one hundred horses to the imperial army at the Emperor's order. According to Simpson, Clari's report may only show that Asen was not a landowner, but a pastoralist. In the autumn of 1185, the Byzantine Emperor Isaac II Angelos encamped at Kypsela in Thrace (now İpsala in Turkey) during his campaign against the Normans of Sicily, who had invaded the Byzantine Empire. Theodor and Asen came to the camp to meet with the Emperor. Byzantine historian Niketas Choniates suggests they came only to provide grounds for their uprising. Clari says, Asen, as the manager of an imperial horse farm, was to come to the imperial court "once a year". Theodor and Asen requested a grant from the Emperor, but its nature is uncertain. The words of Choniates, who recorded the events, suggest they applied for a pronoia (revenues of an imperial estate). On the other hand, a pronoia of little value was seldom granted personally by the monarch. This implies the brothers demanded something more, such as the governorship of a district, or the administration of a semi-independent territory, according to modern scholarly theories. The Emperor rebuffed the brothers' request, but they dared to argue with his decision. Asen, whom Choniates characterized as the "more insolent and savage of the two", was especially impertinent and was "struck across the face and rebuked for impudence" at the command of Isaac II's uncle, John Doukas. They were not detained and could leave the Emperor's camp. Uprising Beginnings A special tax, levied to finance the Emperor's marriage to Margaret of Hungary had brought the Bulgarian and Vlach population to the edge of an uprising before the public humiliation of Asen and his brother at the imperial camp. In spite of the general discontent, the brothers were initially unable to stir up a rebellion, because their compatriots did not believe they had any chance against the imperial troops. Theodor and Asen took advantage of the sack of Thessalonica by the Normans, during which icons of Demetrius of Thessalonica,