Complex sentence: According to Anonymous, Zoltán was born after 903, under his father's second campaign against Menumorut, one of the many local rulers who are solely mentioned in the "Gesta Hungarorum" as opponents of the Hungarians conquering the Carpathian Basin.
Split into simpler sentences: According to Anonymous, Zoltán was born after 903, under his father's second campaign against Menumorut. The latter was one of the many local rulers who are solely mentioned in the "Gesta Hungarorum" as opponents of the Hungarians conquering the Carpathian Basin.