5th century AD

Alaric's Visigoths take Rome in 410, the first time in eight hundred years an outside army has entered the city, and the psychological shock is, if anything, larger than the immediate territorial damage. Pagan critics blame the disaster on Rome's abandonment of its traditional gods for Christianity; Augustine spends more than a decade of this century answering them with the City of God, arguing that earthly cities, however great, are always temporary and secondary to an eternal City of God that Christians build through love of God rather than love of self and worldly power, and that Rome's fall proves nothing about which gods, if any, deserve credit or blame for a city's fortunes.

In China, Buddhism completes a transition this century from an imported curiosity to a fully institutionalized presence with its own direct lines of contact to India. Faxian, a Chinese monk, walks and sails to India and back over roughly fifteen years, writing up the journey not as adventure but as careful testimony about which scriptures and relics he found, noting some sites associated with the Buddha's life already standing empty even as Magadha's monasteries flourish and the faith takes deeper root in China. At Chang'an, the scholar-monk Kumarajiva leads a state-sponsored translation bureau that produces, among a large body of work, a Chinese Diamond Sutra in 402, rendering some of Buddhism's most demanding material, the claim that even the categories a mind uses to grasp reality must themselves be released as empty of fixed essence, into Chinese with a fluency earlier, more improvised translation efforts had not achieved.

Hypatia, who taught mathematics and Neoplatonist philosophy at Alexandria, is murdered by a Christian mob in 415, an event that becomes an enduring symbol of the city's religious and political violence. It does not end Alexandria's intellectual life: the city remains a major center of mathematical, philosophical, medical, and theological scholarship for centuries afterward, and its pagan, Jewish, and Christian communities, which had long competed, overlapped, and shared educational traditions even as this century's conflict intensified, keep doing so after her death rather than ceasing to. At Athens, Proclus keeps a separate Neoplatonist tradition alive in relative isolation, systematizing it in the Elements of Theology into one of pagan philosophy's last great systematic statements before Christian and, later, Islamic thought absorb its method more than its content, though Damascius and Simplicius keep the Athenian school running a while longer still. It is India, this century, that produces the era's most forward-looking scientific work: Aryabhata, writing at the very end of the century in 499, compiles the Aryabhatiya, a compact treatise on arithmetic, algebra, trigonometry, and planetary motion that states, with unusual clarity, that the earth itself rotates on its axis while the heavens only appear to move, a position most of his own successors do not adopt but one now on the record.

Rome's western half does not survive the century as an independent state. Attila leads the Hunnic confederacy to a brief, devastating peak in the 440s and 450s before dying in 453 and the confederacy collapsing almost as fast as it rose; Vandals sack Rome again in 455 and hold North Africa as an independent kingdom; and in 476 the Germanic general Odoacer deposes the last western emperor, a boy named, with unfortunate irony, Romulus Augustulus, an event later historians treat as the western empire's formal end even though contemporaries had little reason to experience it as more decisive than the previous decades' losses. In China, the Northern Wei unifies the fragmented north by 439. And in Armenia, on a scale far smaller than any of this but no less deliberate, Mesrop Mashtots invents an alphabet around 405 built for one purpose, letting scripture and liturgy exist in the Armenian language itself rather than only in Greek or Syriac, a genuinely new technology created explicitly for religious use and documented directly by his student Koriun, a reminder that this century's story is not only large empires falling but also small nations writing themselves into permanent existence for the first time.