Zahumlje got its name from the mountain of "Hum" near Bona, where the river of Buna flowd. It included two old cities: "Bona" and "Hum". Zahumlje included parts of modern-day regions of Herzegovina and southern Dalmatia. Zahumlje's first known ruler was Michael of Zahumlje, he was mentioned together with Tomislav of Croatia in Pope John X's letter of 925. In that same year, he participated in the first church councils in Split. Michael, with grand titles of the Byzantine court as "anthypatos" and patrician ("patrikios"), remained ruler of Zahumlje through the 940s, while maintaining good relations with the Pope.