The Roman emperors were the rulers of the Roman Empire from the granting of the title Augustus to Octavian (pictured) in 27 BC. The English word emperor derives from imperator, an ancient honorific that served as one of the several titles of the emperor. Early emperors ruled behind a republican facade and avoided monarchical titles, but this changed over the following centuries, after which the position became more akin to an absolute monarchy. After the Crisis of the Third Century, the empire was split into a Greek East and Latin West, each with its own emperor. The Western Empire fell to foreign invaders in 476, marking the traditional start of the Middle Ages in Europe. The Eastern Empire, or Byzantine Empire, continued for another thousand years until the Fall of Constantinople in 1453, marking the end of the medieval period, although its power and extent had long been in decline. Several foreign rulers have also claimed the title of Roman emperor, regarding themselves as the true successors to Roman civilization. (Full list...)