According to the work ''De Administrando Imperio'' written by the 10th-century Byzantine Emperor Constantine VII, Croats had arrived in the Roman province of Dalmatia in the first half of the 7th century after they defeated the Avars. However, that claim is disputed, and competing hypotheses date the event between the 6th and the 9th centuries. Eventually, a dukedom was formed, Duchy of Croatia, ruled by Borna, as attested by chronicles of Einhard starting in 818. The record represents the first document of Croatian realms, vassal states of Francia at the time.