Scholars have long studied the so-called Breve chronicon de rebus Siculis as a key source of important historical information, including on the crusade of Frederick II. At the same time, however, this source provides crucial and concrete clues indicative of the typical process involved in the re-writing of chronicles. The work is transmitted by two main manuscripts, in each of which the text varies significantly at several junctures. The conclusion of the Breve chronicon de rebus Siculis, for example, is totally different in the two manuscripts; equally, throughout each manuscript the scribes transmit factual data in remarkably different manners. One example is the passage in which the chronicler describes the destruction of Siponto and the exile of its inhabitants: the years of exile and the names of the sovereigns who allowed their return differ in the two manuscripts, but the changes are absolutely in keeping with the chronology. If we examine this phenomenon objectively, without considering how medieval chronicles actually circulated and how they were copied, at least one of the two texts altered the historical information. However, this text does not constitute a „forgery“ since the philological interpretation of a chronicle is completely different from the interpretation of a document. The writing of history is an integral part of the human experience and anyone who holds a pen in his hands feels compelled to write information on the present and past. But as he retrieves and transcribes information, he also starts to alter it because in the process of composition he ultimately expresses an essential part of himself. Furthermore, a copyist, especially if he is not a professional, selects and summarizes information to adapt it to his own interests and his own worldview.