<P> The Middle Ages are commonly dated from the fall of the Western Roman Empire (or by some scholars, before that) in the 5th century to the beginning of the early modern period in the 16th century, marked by the rise of nation states, the division of Western Christianity in the Reformation, the rise of humanism in the Italian Renaissance, and the beginnings of European overseas expansion which allowed for the Columbian Exchange . </P> <P> Many consider Emperor Constantine I (reigned 306--337) to be the first "Byzantine Emperor". It was he who moved the imperial capital in 324 from Nicomedia to Byzantium, which re-founded as Constantinople, or Nova Roma ("New Rome"). The city of Rome itself had not served as the capital since the reign of Diocletian . Some date the beginnings of the Empire to the reign of Theodosius I (379--395) and Christianity's official supplanting of the pagan Roman religion, or following his death in 395, when the empire was split into two parts, with capitals in Rome and Constantinople . Others place it yet later in 476, when Romulus Augustulus, traditionally considered the last western Emperor, was deposed, thus leaving sole imperial authority with the emperor in the Greek East . Others point to the reorganisation of the empire in the time of Heraclius (c. 620) when Latin titles and usages were officially replaced with Greek versions . In any case, the changeover was gradual and by 330, when Constantine inaugurated his new capital, the process of hellenization and increasing Christianisation was already under way . The Empire is generally considered to have ended after the fall of Constantinople to the Ottoman Turks in 1453 . The Plague of Justinian was a pandemic that afflicted the Byzantine Empire, including its capital Constantinople, in the years 541--542 . It is estimated that the Plague of Justinian killed as many as 100 million people across the world . It caused Europe's population to drop by around 50% between 541 and 700 . It also may have contributed to the success of the Muslim conquests . </P> <P> The Early Middle Ages span roughly five centuries from 500 to 1000 . </P> <P> From the 7th century Byzantine history was greatly affected by the rise of Islam and the Caliphates . Muslim Arabs first invaded historically Roman territory under Abū Bakr, first Caliph of the Rashidun Caliphate, who entered Roman Syria and Roman Mesopotamia . As the Byzantines and neighboring Sasanids were severely weakened by the time, amongst the most important reason (s) being the protracted, centuries - lasting and frequent Byzantine--Sasanian wars, which included the climactic Byzantine--Sasanian War of 602--628, under Umar, the second Caliph, the Muslims entirely toppled the Sasanid Persian Empire, and decisively conquered Syria and Mesopotamia, as well as Roman Palestine, Roman Egypt, and parts of Asia Minor and Roman North Africa . In the mid 7th century AD, following the Muslim conquest of Persia, Islam penetrated into the Caucasus region, of which parts would later permanently become part of Russia . This trend, which included the conquests by the invading Muslim forces and by that the spread of Islam as well continued under Umar's successors and under the Umayyad Caliphate, which conquered the rest of Mediterranean North Africa and most of the Iberian Peninsula . Over the next centuries Muslim forces were able to take further European territory, including Cyprus, Malta, Crete, and Sicily and parts of southern Italy . </P>

European thought during the seventeenth century a.d. like that of fourth century b.c. was marked by