The Rožmberk family legend, which derived the origin of Bohemia´s leading aristocratic dynasty from the Roman Orsini, is usually attributed to Oldřich II of Rožmberk. This attribution however relies on indirect arguments. This article argues that the Orsini claim emerged at least a generation earlier. The conclusion relies on a letter which King Sigismund of Luxembourg addressed to the city commune of Trogir in Dalmatia in 1411 and which contains an allusion to the supposed kinship. The document surveved only as a seventeenth-century copy among papers of the Dalmatian scholar Giovanni Lucio. The internal signs of the writing as well as Lucio´s scholastic profile seem to exclude the possibility that Lucio would have forged it. The early emergence of the claim contradicts neither the broader context of the Orsini legend in various regions of the late-medieval Europe, nor other fifteenth-century documents so far known on the existence of the Orsini myth within the Rožmberk family. These documents, I suggest, shouldbe read in a different way as usual., Petr Maťa., and Obsahuje poznámky pod čarou