In AD 476 a Germanic general named Odoacer deposed the teenage western emperor Romulus Augustulus, sent the imperial regalia to Constantinople and ruled Italy as king. Few people at the time thought the world had ended. Yet that date became the conventional end of the Roman Empire in the West. Why the western empire fell, or whether "fell" is even the right word, is among the most argued questions in history.

Crisis and recovery

The troubles began long before. From AD 235 to 284, in the Crisis of the Third Century, the empire suffered civil wars, invasions, plague and inflation, with more than twenty emperors, most of whom died violently. The silver coinage was debased until it was nearly all copper. The empire recovered under Diocletian, who reigned from 284 to 305. Diocletian divided rule among four emperors, a system called the Tetrarchy, two senior and two junior, so that each frontier had an emperor nearby. He enlarged the army and the bureaucracy and raised taxes to pay for them. After Theodosius I died in 395, the empire was permanently divided between his two sons into eastern and western halves.

The fifth century in the West

Pressure came from peoples beyond the Rhine and Danube, pushed in part by the Huns moving west from the steppe. At Adrianople in AD 378 the Goths destroyed a Roman army and killed the emperor Valens. Rome increasingly settled whole peoples inside the empire as allies under their own leaders. In AD 410 the Visigoths under Alaric sacked the city of Rome, the first time a foreign enemy had taken it in about 800 years, a shock felt across the Mediterranean. The Vandals seized North Africa, the West's richest provinces, in 439, and sacked Rome again in 455. The western government lost its tax base and with it the means to pay armies. The eastern empire, richer and better defended, survived for nearly a thousand more years.

Explaining the fall

Explanations number in the hundreds. Edward Gibbon, in The History of the Decline and Fall of the Roman Empire (1776 to 1789), blamed Christianity and the barbarians in large part, summing up near the end: "I have described the triumph of barbarism and religion." He argued that Christianity drew energy away from public life and the army, and that the empire's very size made it fragile. Later historians stress other forces: overstretched finances and heavy taxes; civil wars that pulled troops from the frontiers; the Antonine Plague of the 160s and later pandemics; and, as Kyle Harper has recently argued, climate change. Many historians now think the West fell because invasion and civil war came together faster than a weakened state could absorb them.

Transformation or collapse?

From the 1970s the historian Peter Brown and others popularized "Late Antiquity" as a vibrant period in its own right, full of religious and cultural creativity. The transformation view holds that the Roman world changed gradually rather than collapsing, as the new kingdoms kept Roman law, Latin and the church. Critics, notably Bryan Ward-Perkins, answered with archaeology: after about 400 in the West, pottery became cruder, coins scarcer, buildings smaller and even cattle smaller, signs of a real fall in living standards. Both sides capture something, and the answer depends partly on whether you look at bishops and books or at farmers and roofs.

Legacy

Rome's legacy is everywhere. Latin developed into the Romance languages, among them Italian, French, Spanish, Portuguese and Romanian, and it lent thousands of words to English. Roman law shapes legal systems across Europe and beyond, and our calendar is a reformed version of Julius Caesar's. Above all, Rome passed on an idea: the republic, in which citizens share power and officials serve limited terms under law. The American founders read Roman history closely, often through Plutarch and Livy. The Federalist essays of 1787 and 1788 appeared under the pen name Publius, after Publius Valerius Publicola, one of the founders of the Roman Republic, while some of their opponents wrote as Cato and Brutus. The United States has a Senate and meets in a Capitol named for Rome's Capitoline Hill, and its founders treated Rome's fall as a warning about armies, ambition and corruption. The legacy has a dark side too: the fasces, the bundle of rods carried before Roman magistrates, gave Mussolini's Fascists their name.

Worked example: Washington as Cincinnatus

In December 1783, after the War of Independence was won, George Washington appeared before Congress, resigned his commission as commander in chief and went home to Mount Vernon. Admirers at once compared him with Cincinnatus. Apply the course's ideas. Washington controlled the only real army in the new nation, and some officers had hinted at using it to pressure Congress. He knew how Caesar's march on Rome had ended the Roman Republic, and he chose the path of Cincinnatus instead. Officers of the Continental Army had formed the Society of the Cincinnati that year, and the city of Cincinnati later took its name from the society. Washington repeated the gesture in 1797, stepping down after two terms as president. The Roman lesson he took was not about columns or conquest. It was that a republic survives when those who hold power give it back.