Roman emperor
The Western Roman Empire collapsed in the late 5th century. Romulus Augustulus is often considered to be the last emperor of the West after his forced abdication in 476, although Julius Nepos maintained a claim recognized by the Eastern Empire to the title until his death in 480. Following Nepos' death, the Eastern Emperor Zeno abolished the division of the position and proclaimed himself as the sole Emperor of a reunited Roman Empire. The Eastern imperial lineage continued to rule from Constantinople ("New Rome"); they continued to style themselves as Emperor of the Romans (later βασιλεύς Ῥωμαίων in Greek), but are often referred to in modern scholarship as Byzantine emperors. Constantine XI Palaiologos was the last Roman emperor in Constantinople, dying in the Fall of Constantinople to the Ottomans in 1453.
History of Rome
Rome's population declined after its peak in the 2nd century. At the end of that century, during the reign of Marcus Aurelius, the Antonine Plague killed 2,000 people a day. Marcus Aurelius died in 180, his reign being the last of the "Five Good Emperors" and Pax Romana. His son Commodus, who had been co-emperor since AD 177, assumed full imperial power, which is most generally associated with the gradual decline of the Western Roman Empire. Rome's population was only a fraction of its peak when the Aurelian Wall was completed in the year 273 (in that year its population was only around 500,000).