History of the Roman Empire
Theodosius was the last Emperor who ruled over the whole Empire. After his death in 395, he gave the two halves of the Empire to his two sons Arcadius and Honorius; Arcadius became ruler in the East, with his capital in Constantinople, and Honorius became ruler in the West, with his capital in Milan and later Ravenna. The Roman state would continue to have two different emperors with different seats of power throughout the 5th century, though the Eastern Romans considered themselves to be the only ones who were fully Roman. Latin was used in official writings as much as, if not more than, Greek and the two halves were nominally, culturally and historically, if not politically, the same state.
Last Roman Emperor
The legend is based on the "Apocalypse of Pseudo-Methodius", which was, after the Book of Daniel and the Book of Revelation, "the most widespread apocalypse story in Europe". It proposes a different Last Emperor from the previous figure, who fought against religious enemies, and introduced the conflict with Islam: he will "go forth against them [the enemies of the faith] from the Ethiopian sea and will send the sword and desolation into Ethribus their homeland, capturing their women and children living in the Land of Promise". After conquering his enemies he would travel to Jerusalem and relinquish his power on the Mount of Olives. The Last Emperor was further developed in the writings of Adso of Montier-en-Der, whose "Libellus de Antichristo" (ca. 954) was a popular biography of the Antichrist, whose coming was preceded by the rise of a Frankish ruler (the continuation of the Roman Empire); this Last Emperor would voluntarily give up his power and die, after which the Antichrist comes to power. Another important impetus came from the oracles of the Tiburtine Sibyl, first recorded in Latin around the year 1000; its legend proved particularly adaptable to rulers all over Europe, containing as it did a list of emperors and kings leading up to the Last Emperor which could be revised or added to as political and dynastic circumstances required. It still had great currency in the fifteenth century.