In the year 527, the man who would be known to history as Justinian the Great set out to rebuild the Roman Empire. By the time he came to the imperial throne in Constantinople, the western empire had been gone for half a century, and the territory he inherited extended no further west than Greece. Justinian wanted to change all that—to roll back to the clock to a time when the empire which still thought of itself as “Roman” actually included Rome.

And so, he sent his armies to conquer Dalmatia and North Africa, before turning towards the cradle of the empire itself. It worked: in May 540, Justinian’s general Belisarius entered the Ostrogoths’ capital at Ravenna, and reclaimed Italy for Constantinople. For a moment, it seemed possible, the Roman Empire was truly back.

The following year, large chunks of the imperial population started swelling up, turning black and dropping dead. Which rather put paid to that idea.

Exactly how many people died in the Plague of Justinian—the words which history links to one’s name are not always flattering—is a matter of some debate. Some more excitable estimates put the death toll as high as 100 million; but that’s over the course of the two centuries or so that the plague recurred. Other estimates have it as low as 25 million. Either way, considering there were only about 200 million people on the entire planet when it started, this was clearly A Big Deal.

It was almost certainly a factor, too, in stymieing Justinian’s restoration. There’s a plausible universe in which Belisarius’ arrival in Ravenna is just the beginning, and what we call “the fall of the western empire” was merely the latest in a line of crises in which bits of imperial territory break away before being forcibly re-attached once again. In this universe, however, the disease-ravaged empire lacked the financial or military resources to hold onto what it had conquered, and within a century the rise of Islam would reshape the Mediterranean completely. And so, even though we generally date the fall of Rome to the year 476, a plague which came 70 years later may be partly responsible for it.

The Plague of Justinian is not the only disease to have radically reshaped the world. Eight centuries later, Europe was hit by what was probably the worst pandemic of all time. The Black Death killed somewhere between 75 and 200 million people.

In just four years—from 1347 to 1351—between a third and a half of the population of Europe died.

That would be world-shaking enough in itself, but it also completely rewrote the social order. Before the Black Death, European society had for centuries been structured around what we’d later call feudalism: to over-simplify massively, the system by which poorer people would work for richer ones in exchange for access to their land, and put up with having no freedom of movement because otherwise they didn’t eat.

But when plague caused the population to collapse, food and land prices plummeted, too. Land without workers turned out to be worthless, so the lords found themselves competing for labourers. Despite assorted ruling class efforts to overcome the laws of supply and demand, wages rose, and keeping peasants tied to particular scraps of land proved impossible. The Black Death didn’t just kill people. It probably killed feudalism, too.

It’s too early to know how coronavirus might reshape 21st-century society. But we can certainly speculate. Perhaps, as large chunks of the workforce simultaneously shift to working from home for the first time, it’ll kill the idea that you need to be in the office to get stuff done. If it turns out that employees will do their work even if they’re not literally in their managers’ line of sight, bosses could finally shake their addiction to presenteeism.

That could have all sorts of unpredictable knock-on effects: less pressure on transport networks, lower emissions, even relief for overheated housing markets as people discover they can live further from work. Or perhaps it could drive an increase in mothers’ participation in the workforce: more flexible office culture, after all, would make it easier to combine work with caring responsibilities.

In politics, meanwhile, Europe’s apparent indifference to the spiralling crisis in Italy might undermine support for the EU in a way that a piffling thing like Brexit never could. Across the Atlantic, the realities of dealing with a pandemic in a country where millions can’t afford health insurance might finally move universal healthcare from the realm of left-wing radicalism to that of obvious common sense.

Perhaps this crisis will even be the thing that kills off the Reagan/Thatcher economic model at long last. For forty years, governments have shifted more and more risk from state or employers onto individuals in the name of economic competitiveness, apparently on the assumption that the only way of motivating people to work is ensuring they’re terrified of starving to death by some bins.

Now that a fear of financial ruin might drive sick, contagious people to work when they should be in isolation, perhaps we can go back to talking about the state as the enabler of our freedoms rather than the barrier to them.

Or perhaps it won’t: where this will take us, we just don’t know, and your guess is as good as mine. But pandemics have been reshaping the world in unpredictable ways throughout history. If this crisis is even a fraction as serious as it seems, don’t be surprised if the world afterwards looks very unlike the world before.