The Roman Empire did not fall all at once, and only half of it fell in the fifth century. After the crisis of the third century, emperors from Diocletian onwards split the work of ruling between East and West, and after Theodosius I died in 395 the two halves were never ruled by one man again. The Western half, weaker and poorer, lost control of its provinces to Germanic groups such as the Goths and Vandals over about eighty years: the Goths defeated a Roman army at Adrianople in 378 and sacked Rome in 410. In 476 Odoacer deposed the last Western emperor, Romulus Augustulus. The Eastern half, ruled from Constantinople, lasted until the Ottoman conquest in 1453.

This guide takes the story in the order an exam answer needs it: the long-term weaknesses, the split, the crises of the fifth century, then the argument about why.

First, which empire and which fall

The most common mistake in this topic is asking "why did Rome fall?" as if there were one Rome and one date. There were two halves by the end of the fourth century, with two emperors, two capitals and two very different fates.

• The Western Roman Empire, ruled latterly from Milan and then from Ravenna (from 402), covering Italy, Gaul, Spain, Britain and North Africa. It ceased to exist as a political unit in the fifth century, conventionally in 476.
• The Eastern Roman Empire, ruled from Constantinople, covering the Balkans, Greece, Anatolia, Syria, Palestine and Egypt. Historians later called it the Byzantine Empire, but its people called themselves Romans throughout. It lasted until 29 May 1453.

So the real question an exam asks is usually narrower: why did the Western empire collapse in the fifth century while the Eastern empire survived?

The crisis of the third century

From 235, when the emperor Severus Alexander was murdered by his own troops, to 284, the empire came close to breaking apart. Historians call this the crisis of the third century. Its features:

• Rapid turnover of emperors. Dozens of men claimed the throne in about fifty years, most of them generals proclaimed by their armies, and most of them died violently.
• Pressure on two frontiers at once. Germanic groups crossed the Rhine and Danube, and a new and aggressive Persian dynasty, the Sasanians, attacked in the east. In 260 the emperor Valerian was captured by the Persian king Shapur I.
• Breakaway states. For a time the Gallic Empire in the west and the Palmyrene Empire under Queen Zenobia in the east ruled large parts of Roman territory, before the emperor Aurelian reunited them in the early 270s.
• Money trouble. Emperors paid the army by debasing the silver coinage, and inflation followed.
• Plague. An epidemic often called the Plague of Cyprian struck from around 249 into the 260s.

The split, step by step

Diocletian (ruled 284 to 305) ended the crisis and reorganised the empire. In 293 he set up the Tetrarchy, a system of four rulers: two senior emperors (Augusti) and two junior ones (Caesares), each responsible for a region. He also enlarged the army and the bureaucracy and reformed taxation. This was the first formal division of the work of ruling between East and West.

Constantine (ruled 306 to 337) reunited the empire under one ruler by 324 after civil wars. He supported Christianity (the Edict of Milan of 313 granted toleration) and in 330 dedicated a new capital at Byzantium, renamed Constantinople. It sat on the Bosphorus, between Europe and Asia, and became the Eastern capital.

Theodosius I (ruled 379 to 395) was the last emperor to rule both halves. In 380 he made Nicene Christianity the official religion of the empire. When he died in 395, the empire passed to his two sons: Arcadius in the East and Honorius in the West. Each half had its own court, army and administration from then on.

The Goths, the Huns and the fifth century

In the 370s the Huns, nomads from the steppe, moved west and pushed Gothic groups towards the Danube. In 376 the emperor Valens allowed many Goths to cross into Roman territory. Mistreated by Roman officials, they rebelled.

What happened in 476. Odoacer was a Germanic commander of the army in Italy. He deposed the teenage emperor Romulus Augustulus, did not name a replacement, and sent the imperial regalia to the Eastern emperor Zeno in Constantinople, ruling Italy as king while formally acknowledging the Eastern emperor. The Senate kept meeting, Roman law continued, and Odoacer's successor Theodoric ruled with Roman officials. That is why historians treat 476 as a symbolic date, not a single collapse. Some prefer 480, when Julius Nepos, a Western emperor still recognised by Constantinople, died.

The loss of North Africa in 439 is often the more important date for historians. The Western government depended on taxes and grain from Africa to pay its armies. Without them, it had to rely more on paying Germanic allies to fight for it, which made those allies more powerful.

Why the East lasted another thousand years

The Eastern half faced the same Huns and Goths. It survived because it had advantages the West did not.

• Wealth. Egypt, Syria and Anatolia were richer, more urban and paid more tax.
• Constantinople's defences. The city sat on a peninsula protected by sea, and the Theodosian Walls, built in the early fifth century under Theodosius II, held off attackers for centuries.
• Geography. The East had a shorter, more defensible frontier on the Danube and could use its navy and its gold to divert invaders westwards, which is partly what happened with the Goths.
• A stable rival. Its main enemy, Persia, was a state it could negotiate with, not a series of migrating groups.

How historians weigh the causes

There is no agreed single cause. A strong essay names the main interpretations and judges between them.

Edward Gibbon. His The History of the Decline and Fall of the Roman Empire (six volumes, 1776 to 1789) shaped the debate for two centuries. He saw a long moral and political decline, blaming among other things the loss of civic virtue, the reliance on non-Roman soldiers, and Christianity, which he thought turned energy away from the state.

Transformation, not fall. From the 1970s, Peter Brown and others developed the idea of late antiquity: a long period of change in which Roman, Christian and Germanic cultures blended, rather than a catastrophe. On this view, the kingdoms that replaced Western Roman rule kept much of Roman law, language and religion.

Back to a real fall. In 2005 two books pushed back. Peter Heather's The Fall of the Roman Empire argued that external pressure, set off by the Huns, was decisive, and that the empire was not fatally weak before it arrived. Bryan Ward-Perkins's The Fall of Rome and the End of Civilization used archaeology (pottery, coins, building quality) to show that living standards in the West fell sharply after Roman rule ended.

Climate and disease. More recently Kyle Harper's The Fate of Rome (2017) has added epidemics and climate change to the list of pressures.

Structure: internal weaknesses (political instability, money, the size of the empire), external pressure (Huns, Goths, Vandals, Persia), and the turning points that made them fatal (Adrianople, the loss of Africa), ending with a judgement about which was decisive. How to explain a timeline in a video covers how to show long and short-term causes on one line.

Mistakes that lose marks

• Writing that "Rome fell in 476" without saying which half. Always say the Western empire.
• Treating the Germanic groups as one people or as simple destroyers. Goths, Vandals, Franks and others were different groups, often fighting for or with Rome, and many wanted a share of the Roman system, not its end.
• Blaming Christianity alone. The Eastern empire was at least as Christian and survived.
• Forgetting the East entirely. A question on the fall is half answered without explaining why Constantinople survived.

A scene plan for a five minute video

1. A map of the whole empire in 117, at its largest, one colour.
2. The third century: emperors' faces appearing and being crossed out in quick succession, arrows pressing on two frontiers.
3. Diocletian's four rulers, each placed on part of the map; the map splits into East and West.
4. Constantinople drawn on the Bosphorus, walls going up.
5. 395: the map tears down the middle, Arcadius on one side, Honorius on the other.
6. The Huns arriving from the east, pushing the Goths across the Danube; Adrianople marked with a crossed sword.
7. The West shrinking, province by province, as Vandals, Visigoths and others take Gaul, Spain and Africa; 410 and 455 marked on Rome.
8. 476: Odoacer sending the regalia east in a box.
9. The East still standing, the line running on to 1453.
10. Gibbon, Brown, Heather and Ward-Perkins as four small portraits, each with one sentence.

For the craft of a history video like this, see how to make a history explainer video, and for a presentation due tomorrow, how to make a timeline video for history class.

Make your own version for class

1. 1

   Set your question

   Decide whether your video answers why the West fell, why the East survived, or both. Write that question as the first line of the script.

2. 2

   Build the timeline first

   Use the table above. Pick the eight to ten dates your course expects and put them in order before you write any narration.

3. 3

   Write one paragraph per scene

   Follow the scene plan above. About 750 words is five minutes at roughly 150 spoken words a minute. End with your own judgement on the main cause.

4. 4

   Paste the script into openCanviz

   Choose Keep my wording so names and dates are said exactly as you wrote them, set a target length, and try the painted or poster style for maps and portraits.

5. 5

   Check every date and map

   Pause on each scene. Drafted maps can put Ravenna in the wrong place or label the Visigoths as Vandals. Fix any wrong label in the editor.

Common questions

When did the Roman Empire fall? The Western Roman Empire is conventionally said to have ended in 476, when Odoacer deposed Romulus Augustulus. The Eastern Roman Empire, often called the Byzantine Empire, lasted until the Ottoman conquest of Constantinople on 29 May 1453.

What was the main reason the Western Roman Empire fell? Historians disagree. Most combine internal weaknesses (unstable government, financial strain, a vast frontier) with external pressure from the Huns and Germanic groups, and point to turning points such as Adrianople in 378 and the loss of North Africa in 439. Peter Heather stresses external pressure; others stress internal problems.

Who sacked Rome in 410? The Visigoths, led by Alaric. It was the first time in about 800 years that the city had been taken by a foreign enemy, and it shocked the Roman world, prompting Augustine of Hippo to write The City of God.