The castle of "Byhor", or Bihar (now Biharia in Romania), was the center of the duchy of Menumorut at the time of the Hungarian conquest of the Carpathian Basin in the 890s, according to the "Gesta Hungarorum". The "Gesta"—the only primary source which mentions Menumorut—describes him as a ruler "with Bulgarian heart" who was the vassal of the Byzantine Emperor. Menumorut's subjects were Khazars, and the Székelys joined the invading Hungarians in his duchy. Historian Tudor Sălăgean writes that other peoples (including Romanians) must have also lived in Menumorut's realm. Menumorut was forced to give his daughter in marriage to Zoltán, son of Árpád, Grand Prince of the Hungarians. When he died, his son-in-law inherited his duchy. Modern scholars debate whether Menumorut and his duchy actually existed or the anonymous author of the "Gesta" invented them. For instance, historian György Györffy says that Menumorut's name preserved the memory of the Moravians who dominated parts of the Carpathian Basin in the . According to historians György Györffy and Victor Spinei, the presence of Kabars in the region could have given rise to Anonymous' reference to Menumorut's "Khazars".