Letters before legions
Christianity conquered no armies in its first three centuries; it had none. It spread the way gossip spreads: along roads and sea lanes, carried by merchants, soldiers, and enslaved people into the empire’s cities, organised by letters — Paul’s epistles are administration by post — and made attractive by charity that fed strangers during plagues when pagan priests fled. By 300 CE perhaps one in ten Romans called themselves Christian. Then Constantine, before a battle in 312, decided the Christian God backed winners. Imperial favour — money, basilicas, an end to persecution — did in a generation what three centuries of witness had prepared. Patronage transforms: approval can matter more than belief.
Islam moved faster still. From the Hijra in 622, Arab armies carrying a new revelation took Persia, the Levant, Egypt, North Africa, and Spain within a century — and the conquests hardened into something more durable than garrisons: one Arabic language of law and learning, one pilgrimage road to Mecca pulling scholars from three continents, and cities like Baghdad where translators rendered Greek philosophy, Indian mathematics, and Persian astronomy into Arabic side by side. When paper-making arrived from Central Asian prisoners in 751, the caliphate’s bureaucracy and book market drank it up; Cairo and Córdoba built libraries while much of Western Europe kept a few chained Bibles.12
- 312 CE Constantine favours Christianity
- 622 The Hijra; the Islamic calendar begins
- 751 Paper-making reaches the Abbasid world
- c. 800 Baghdad’s House of Wisdom flourishes
- 1054 The churches of East and West split
- 1204 Crusaders sack Constantinople
The road that carried everything
The Silk Roads were never one road but a braided system of caravan tracks, sea lanes, and relay oases — and they carried ideas more consequentially than silk. Buddhism walked them into China, transforming both the faith and its host. Paper, gunpowder, and the compass travelled them west. Tang Chang’an, the world’s largest city around 750 with perhaps a million people, held Persian wine shops, Central Asian musicians, Nestorian churches, and mosques: a cosmopolitan capital is the fingerprint of open trade. Even diseases commuted — the plague of Justinian in the 540s likely rode these same routes, a rehearsal for worse to come.11
The split that stuck
In 1054, Rome and Constantinople excommunicated each other over doctrine, leavened bread, and who commanded whom — the Great Schism. It might have healed, until the Fourth Crusade, bankrupt and diverted, sacked Christian Constantinople in 1204 and carried its treasures to Venice. Schisms have dates and deeds: 1054 drew the line, 1204 dug the trench. When Constantinople finally fell to the Ottomans in 1453, Moscow would call itself the Third Rome — the argument about who inherits an empire outliving the empire by centuries.