Why did the Eastern Roman Empire survive when the West fell?

Two halves, two fates

When Emperor Theodosius died in 395, his young sons divided the Roman world. Arcadius ruled the East from Constantinople, Honorius the West. Both halves kept the same laws, the same gold coins and the same name: Roman. Eighty years later the West was gone, as why the Roman Empire fell explains. The East still held the Balkans, Anatolia, Syria and Egypt, and it went on for almost another thousand years.

The money was in the East

The eastern provinces were older, thick with cities and far richer. Egypt’s grain fleets fed the capital. Anatolia and Syria paid their taxes year after year, because invaders rarely stayed there long. That income let the East lose an army and pay for another. It did exactly that in 378, when the Goths destroyed Emperor Valens and most of his field army near Adrianople, today’s Edirne.

Scarcely one-third of the whole army escaped. Nor, except the battle of Cannae, is so destructive a slaughter recorded in our annals; though, even in the times of their prosperity, the Romans have more than once had to deplore the uncertainty of war.

By 382 Theodosius had made peace and settled the Goths inside the empire as allies. The West had no such reserves. It lost its tax base one region at a time: Britain, most of Spain and Gaul, and in 439 North Africa, seized by the Vandals.

A capital nobody could take

Constantinople had water on three sides: the Sea of Marmara, the Bosporus and the deep harbor of the Golden Horn. The fourth side was closed in 413 by the land walls of Theodosius II, which grew into an inner wall, a lower outer wall and a moat over 20 meters wide, running some 5.7 kilometers (3.5 miles) across the peninsula. When an earthquake threw down long stretches in 447, with Attila’s Huns in the Balkans, the city’s chariot-racing factions rebuilt them in about sixty days.

Avars and Persians besieged the city in 626, an Arab army and fleet in 717–718. Both failed; the Arab ships burned under Greek fire, a liquid flame sprayed from Byzantine galleys. No foreign enemy got inside until the Crusaders in 1204, and the final blow needed Ottoman cannons (when Constantinople fell).

Gold to send the danger west

The East could also pay its enemies to leave. By the peace of 443 it owed the Huns 6,000 Roman pounds of gold at once and 2,100 a year. Humiliating, but cheaper than losing Thrace. When the new emperor Marcian stopped paying in 450, Attila turned on the West: Gaul in 451, Italy in 452. The Goths drifted the same way. Alaric plundered Greece in the 390s, then moved on to Italy. In 488 Emperor Zeno sent Theodoric and his Ostrogoths to Italy to fight Odoacer, the king who had retired the last western emperor.

Emperors who stayed in charge

After 455 the West was run by generals such as Ricimer, who made and unmade puppet emperors. The East had overmighty generals too, but its emperors sat in one fortified capital with a large civilian staff, and they could strike back: in 471 Leo I had his Alan general Aspar killed in the palace. The throne never left Constantinople. Its people called themselves Romans until the very end.