Before King Arthur, there was Excalibur.

During the Fall of the Roman Empire, its last emperor, 12-year-old Romulus Augustus (Thomas Sangster), rules for a day before losing all that he loves: his family, his home and an empire that once stood for truth and honor. Imprisoned on the island-fortress of Capri, Romulus, aided by the clever strategies of his teacher Abrosinus (Ben Kingsley) and the heroic skills of his legionnaire Aurelius (Colin Firth), escapes the island. Accompanied by his friends and a mysterious envoy from Constantinople, Romulus travels to Britannia in search of the Last Legion - the fabled Dragon Legion. There, Romulus will fight alongside his friends to make his last stand for Rome, and take his first steps to becoming the man and the king who started the Arthurian legend.