Subiect: czar Boril, the usurper of the throne. In order to defeat it, he resorted to the help of Hungarian king Andrew II. The Transylvanian military expedition (Saxons, Szekelys, Vlahs and Pechenegs) organized against the rebels in Vidin and led by count Ioachim of Sibiu is described in a royal diploma issued years after the event by the chancellery of king Bela IV on 23 June 1250, from Györ. Directed from the political centre in Preslav, the actions for the liberation of the Empire from the influence of Boril began with the boyars’ uprising in Vidin and despite the initial failure they continued with an amazing success. The unfortunate czar, allied with Hungary and the Latin Empire, was forced to barricade himself in the Tsarevets fortress, where he was besieged by Ivan Asen II. Given that the Latins in Constantinople and the Hungarians could not help the czar besieged in Tarnovo, at the beginning of 1218 Ivan Asen occupied the capital-city of Tarnovo and overthrew Boril.
