Complex sentence: He claimed that Publius Libonus, Roman commander who fled from Julius Cesar (and supposedly settled down in Lithuania), was ancestor of Lithuanian and Ruthenian rulers, and that the name of "Livonia" comes from "Libonus".
Split into simpler sentences: He claimed that Publius Libonus, Roman commander who fled from Julius Cesar and supposedly settled down in Lithuania, was ancestor of Lithuanian and Ruthenian rulers. Supposedly the name of "Livonia" comes from "Libonus".