One does not normally expect to open Procopius and find the apocalypse. His prose, for all its invective, is typically concerned with the slow grinding of Roman ambition against the resistance of lesser peoples. Yet tucked between his accounts of Gothic war and imperial orgies is a moment of world-historical eeriness: a year in which the sun lost its fire and the world, in wholly literal sense, went dim.

“In this year,” he wrote, “the sun gave forth its light without brightness, like the moon, during the whole year, and it seemed exceedingly like the sun in eclipse, for the beams it shed were not clear nor such as it is accustomed to shed” (Wars 4.14.5–6; ἥλιος ἐν ἔτει τούτῳ ἄνευ τοῦ συνήθους αὐγῆς ἔλαμψεν, ἀλλ’ ἤδη τῷ μηνὶ προσεοικὼς κατὰ πάντα τὸν ἐνιαυτόν).

Modern scholars have dubbed this the “536 Event”—an innocuous name for what is now considered the most dramatic climatic downturn of the last two thousand years. What follows is an account of what likely happened, how we know, and what followed when the skies grew dark.

1. Scholarly Discovery: The Fog Begins to Lift

Though usually mentioned, if in passing, in the standard histories of the period, the 536 event didn’t come clearly into view until the 1980s. NASA scientists Richard Stothers and Michael Rampino were the first to draw connections between ancient reports of sun-dimming and sulphate layers in polar ice cores. Their work, published in the Journal of Geophysical Research (1983), suggested a major volcanic eruption might have caused a stratospheric dust veil.

Tree ring chronologies from Ireland and Scandinavia soon confirmed a sharp drop in temperature, not just in 536, but again in 540 and 547. Ice cores from both Greenland and Antarctica reinforced the picture. What had once looked like local fog now looked like global catastrophe.

1. The View from the Sixth Century

The ancient texts are brief but chilling. You’ve had Procopius, but Cassiodorus, the Roman bureaucrat writing from Ravenna, observed that the sun had lost its “wonted light” and appeared “bluish,” casting shadows at noon no more than moonlight would. The seasons were distorted, the harvests pitiful. “We marvel to see no shadows of our bodies at noon,” he writes—”the rays of the sun hardly thin and wanting, the moon shining without brightness.” (Variae 11.10; solis radius vix tenuis et exiguus, et luna sine fulgore pallescens).

John the Lydian describes the sun as dimmed for nearly a year, blaming “moisture” in the atmosphere (De Ostentis 70; τὸν ἥλιον σκοτίζεσθαι διὰ τὴν ἀτμώδη φύσιν τῆς ἀνιγμένης ὑγρότητος). John of Ephesus, more dramatic still, writes that the sun “gave forth its light without brightness… and it seemed extremely like the sun in eclipse” and that its rays were visible only for two or three hours a day.

In China, the Nan Shi records yellow dust, summer snow, and crop failures. The Gu Jin Tu Shu Ji Cheng documents severe frosts in midsummer and strange red skies. I will repeat: these were not reports of isolated events, but must be seen as evidence of a single and massive disruption of our planet’s atmosphere.

III. Causes: Fire from Earth or Stone from Heaven?

For decades, the leading theory has been volcanic eruption—perhaps more than one. Sulphate spikes in the ice core record suggest a massive tropical eruption in 535/6, followed by another in 539/40. Some suspect the Ilopango caldera in El Salvador; others, a candidate in Indonesia. But no crater has yet been definitively linked to the 536 event.

Then there is the asteroid hypothesis. Proposed in the 1990s by dendrochronologist Michael Baillie, it posits that the dimming of the sun may have been caused by an extraterrestrial impact—a comet disintegration or oceanic airburst.

Supporting this are the spherules, high concentrations of calcium carbonate, and tropical marine microfossils discovered in Greenlandic ice dated to the 530s. These may indicate a comet or asteroid struck the sea, casting a vast quantity of marine material into the atmosphere. Some even speculate the impact formed the Gulf of Carpentaria in northern Australia.

The impact theory is no longer in vogue, but it has not been disproved. Indeed, the lack of a definitively identified volcanic source lends it continued, if cautious, relevance.

1. A Decade of Chilling Consequences

Whatever happened in 536, tree ring data from across the Northern Hemisphere point to a significant drop in average summer temperatures between 536 and 550 AD. This was not a brief dip. It was the coldest decade in at least 2,000 years. The Palgrave Handbook of Climate History describes this period as the Late Antique Little Ice Age, a term coined to acknowledge both its severity and historical impact.

In Italy, famine followed crop failures. The Liber Pontificalis reports mothers eating their children. In Gaul, Gregory of Tours mentions pestilence and starvation. In Constantinople, Procopius records panic and theological speculation. The empire, engaged in a costly reconquest of Italy under Justinian, found itself overstretched. Supply lines faltered, soldiers deserted, and recruitment collapsed. The general Belisarius, once the hammer of the Vandals, was recalled and replaced.

As if this were not enough, plague broke out. In 541, the first wave of the Justinianic Plague devastated the Eastern Empire, killing perhaps a third of the population. Although the exact link between the cooling and the pandemic is still debated, ecological stress and malnutrition likely contributed to its rapid spread.

The geopolitical fallout was substantial. The faltering of Justinian’s campaigns meant that Italy was never fully reintegrated into the Empire. The weakening of imperial infrastructure may have contributed to the slow-motion collapse of Roman influence in the West. In the East, economic strain and demographic decline set the stage for the Arab conquests of the seventh century.

The Chinese sources suggest a similar pattern: famine, depopulation, and dynastic instability. The Wei and Liang courts faced increasing peasant unrest, and the Sui unification, once seen as a triumph, was built atop foundations laid by climatic misery.

Conclusion: A Cold Reminder

The 536 Event was not just a curiosity for specialists. It was a moment when nature took control of history. Whether caused by volcano, asteroid, or some grim cosmic collaboration, the sun dimmed and the world changed.

And yet the cloud has lifted not only from the sun, but from our own understanding. It is no longer a mystery. It is a case study in what happens when the skies go wrong: when ash or stone—or both—intervene in the course of civilisations.

My final observation? Something that hasn’t made its way into my essay is the long run of new laws made by Justinian—remissions of unpaid and unpayable tax, reorganisations of imperial defence along the Danube, and so forth. The Imperial Government did all it could to mitigate a disaster that no one could remotely understand. It didn’t do badly by historical standards. Yet a third of the Empire’s population still died when the plague rolled along five years later. If something like this were to happen today, would our own supposedly omnicompetent rulers do any better? Looking at how they behaved in 2020, I rather suspect they would make things worse, not better.

Note: I’ve given Greek and Latin sources in the original when I could track them down. For the Chinese material, my thanks to Sebastian.

Primary Sources

• Cassiodorus. Variae. Ed. T. Mommsen. MGH AA vol. 12. Berlin: Weidmann, 1894.
• John of Ephesus. Ecclesiastical History, in Chronicle of Zuqnin, pt. 3. Trans. Witakowski. Liverpool: Liverpool University Press, 1996.
• John the Lydian. De Ostentis. Ed. R. Wachsmuth. Leipzig: Teubner, 1898.
• Procopius. Wars. Trans. H.B. Dewing. Loeb Classical Library. London: Heinemann, 1914.
• Nan Shi and Gu Jin Tu Shu Ji Cheng. Chinese Histories.

Modern Scholarship

• Baillie, Michael. A Slice Through Time. London: Routledge, 1995.
• Büntgen, U., et al. “Cooling and Societal Change.” Nature Geoscience 9 (2016).
• Keys, David. Catastrophe. London: Century, 1999.
• Newfield, Tim. “The Global Cooling Event of the Sixth Century.” HistoricalClimatology.com, 2016.
• Stothers, R., and M. Rampino. “Volcanic Eruptions in the Mediterranean.” JGR 88 (1983).
• White, Sam et al., eds. Palgrave Handbook of Climate History. London: Palgrave Macmillan, 2018.