There is no shortage of excellent books about the current pandemic and how we got here, but if you seek an entertaining yet sober account of how the world has dealt with lockdowns in the past and how we can better protect ourselves in the future, you should read Until Proven Safe: The History and Future of Quarantine.

Geoff Manaugh and Nicola Twilley began work on the book years ago, which, luckily for us, allowed them to travel around the world in their quest to understand the uses of quarantine over the centuries. They have produced a superb story—part travelogue, part science, part history, and wholly fascinating.

JIM KELLY: Before the pandemic took hold, early last year, it is fair to say that not many people were thinking about quarantines. Yet, as you vividly recount in your book, as soon as the notion of a possible quarantine became discussed, lots of folks had a visceral reaction against it. Why was that so?

GEOFF MANAUGH: There has always been an air of fear or dread around the notion of quarantine, precisely because it deals with suspicion and uncertainty—a person is only in quarantine if they don’t know whether they are sick. If you know you’re sick, that’s isolation, not quarantine. Even the word “quarantine” has a strange, exotic aura to it. It’s interesting to note that, when a horror movie came out back in 2008, it was simply called Quarantine, as if the word itself was enough to inspire fear.

Manaugh and Dr. Luigi Bertinato of the Verona Health Authority wear plague gear from the coronavirus and Black Death eras.

As we explore in the book, quarantine also has a long conceptual tie to monsters and the unknown—to novel, incurable diseases as well as to the people, animals, and plants potentially bearing those diseases. For example, we describe the myth of “Alexander’s gates” as a quarantine allegory—colossal iron doors supposedly built by Alexander the Great in the Caucasus Mountains to keep Eastern monsters out of the European world.

But what’s interesting about this is that, if quarantine is a way to protect ourselves from monsters—“the other,” however that is defined—what does it mean when we quarantine ourselves? Are we potentially the monsters now? For many people, this is a reversal of how they normally think of themselves or their place in the world: European travelers in the 19th century often regarded themselves as the civilized ones—safe, clean, and free of disease—only to be quarantined upon returning from a foreign destination. In quarantine, we wait to see if we are the ones who are diseased and dangerous—to see whether an invisible monster will emerge from within.

J.K.: Quarantine, which as you point out is derived from the Italian phrase meaning “40 days,” has a long and durable history. How did its use first come about?

NICOLA TWILLEY: Historians trace the first mandatory public-health measures with specific provisions for quarantine back to July 1377, shortly after the Black Death first arrived in Europe. Officials in Dubrovnik (then known as Ragusa, and part of the larger Republic of Venice) proclaimed that anyone arriving from “plague-infested areas” would not be allowed to enter the city until they had spent a month on a nearby island. It was a compromise solution: rather than shut down trade—the city’s economic lifeblood—in the face of this terrifying new disease, officials simply inserted a spatiotemporal buffer, delaying the arrival of potentially infected people and goods until they were proven safe.

Twilley sits inside a Trexler isolation unit.

This initial 30-day waiting period was quickly extended to 40 days, or a quarantena, in the Venetian dialect, as a way to conceptually backdate the practice to a number that had religious significance—think of Christ’s 40 days in the desert or the 40 days of rain in the story of Noah’s ark.

J.K.: You do a marvelous job in describing how Venice, even though it lost two-thirds of its population to the Black Death in the 14th century, coped more effectively than other parts of the world. What did Venice do differently?

N.T.: Quarantine was first mandated in Dubrovnik, but it was refined into an architectural and spatial science in Venice itself. The question of “Why Venice?”—why the formal practice of quarantine emerged there rather than in any of the other regions that were devastated as the Black Death spread westward from Asia—is endlessly intriguing. Part of it has to do with the topography of the city itself: Venice is an archipelago of islands connected by boats and bridges, which makes it a natural laboratory for experimenting with new forms of isolation. (Later, Venice also created Europe’s first official “ghetto,” applying the spatial logic of sanitary isolation to control its Jewish population.)

G.M.: Another factor was a willingness to embrace a secular, even scientific explanation for the plague, that the disease’s spread might have more to do with spatial proximity than religious or astrological explanations. If you think a disease is caused by the stars, then the spatial logic of quarantine—just putting people in separate rooms—makes no sense. Quarantine, in this regard, is quite a modern approach to controlling and containing the unknown.

N.T.: Finally, Venice wasn’t a hereditary monarchy or a feudal state: it was a republic, where at least some citizens had the power to elect their leader. That democratic spirit carried over into a commitment to civic virtue, and a willingness to invest in the common good—for example, by building and funding collective quarantine facilities.

J.K.: One tends not to think of quarantining animals or vegetables if they have been exposed to a deadly disease; they are simply destroyed. But there are pockets where efforts are being made to ensure that an infectious disease does not wipe out an entire species. Which I believe leads us to chocolate! Can you explain?

N.T.: Certainly, although we should apologize in advance: in case you need something else to worry about, let us introduce you to the chocopocalypse! This is the very real threat that the world’s cocoa harvest will be decimated by one or more of any number of dreadful diseases that affect cacao plants in different regions of the world. Quarantine is the shield helping us to avoid that hideous fate while still allowing agronomists and plant breeders to move cacao plants around for research purposes.

The first quarantine took place in Dubrovnik, where anyone arriving from “plague-infested areas” had to first spend a month on nearby Lokrum.

Curiously, the world’s cocoa-quarantine facility is located in Reading, in the very untropical suburbs of London, England. Ninety-five percent of traveling cacao plants have to spend a two-to-three-year layover in a greenhouse there, being monitored for signs of disease. For a certain class of high-value, disease-prone tropical crop, this kind of climatic quarantine makes a lot of sense—banana plants are hosted by Belgium, where there are no local banana plantations that might be at risk of imported pathogens, and rubber trees often quarantine in U.S.D.A. greenhouses in Maryland, which any rogue tropical pests would find quite inhospitable.

J.K.: And now for a question far less sweet. You also visited the Waste Isolation Pilot Plant, with the slightly whimsical acronym WIPP, which is built deep in a New Mexico salt mine and is so far, as you describe it, the only “active facility for the permanent, deep geological disposal of nuclear waste.” Can you describe a bit how the government plans to mark this site as dangerous for visitors a thousand years from now?

G.M.: Our visit to WIPP was a peculiar highlight of our travels, from the diesel fumes of heavy machinery working 2,000 feet below ground to the briny, salt taste on our lips as we walked through the corridors, which are poetically known as “drifts.” But beyond the strangeness of the place itself, plans to mark the site are at least as surreal.

In the 1980s, the Department of Energy convened a panel of experts, including linguists, specialists in radiation sickness, anthropologists, and more, to come up with a way to communicate the danger of radioactivity to people living thousands, even tens of thousands, of years from now.

The results ranged from gigantic earthworks, such as concrete thorns, meant to scare people away, to a plan to genetically modify domestic house cats so that their skin would turn fluorescent in the presence of radiation. One group, at a nuclear-waste conference we attended in Phoenix, even proposed creating a legacy Web site, accessible by smartphone, apparently without ever considering that people 10,000 years from now might not still have phones, let alone AT&T or good Wi-Fi.

In the end, multi-ton granite blocks carved with messages will be the main warning sign for future generations—amusingly, the Department of Energy points out that the quality of their granite is better than Stonehenge’s.

J.K.: There is much research being done now about how to predict future virus outbreaks, especially now that global travel can make two cities on two different continents as contagious to each other as if they were a block apart. This can allow us to introduce quarantines before the disease creates widespread damage and not after. Do you think the public is ready for this?

G.M.: One of the challenges we face now, as we appear to be moving out of the coronavirus pandemic, is not to move on so quickly that we erase it from our memories. We need to pause now and look back at what did and did not work, and use that insight to prepare for the next pandemic—and the next quarantine—precisely so that the public is ready for it.

More to the point of your question, in the book we look at the rise of networked sensors, like voice-activated speakers and other “smart home” technologies, that are often used as medical diagnostic tools. Amazon has already patented a way for Alexa, its digital assistant, to recognize signs of sickness in the sounds of people coughing nearby, and Google, of course, has long been experimenting with ways to predict flu patterns based on people’s Internet searches, purchase histories, and more.

What we describe in the book is a realistic but quite ominous, even dystopian, world in which your smart home, with all of its gadgets, hooked up to your Internet search history, might have the power to keep you inside—what we call predictive or algorithmic quarantine.

J.K.: “In the coming decades,” you write, “we will almost certainly find ourselves more dependent on quarantine, not less.” And thus, you say, we must redesign it. What might I do to prepare myself for quarantine, including designing a good space for myself?

N.T.: By the end of all our research and reporting, we were thoroughly convinced that we are indeed entering a new age of quarantine—and that this medieval public-health measure needs to be completely redesigned and reimagined for the 21st century.

In the book, we tell the stories of a handful of people who, prior to the coronavirus, had dedicated considerable time and effort to making sure that modern ideas about human rights and health equity were built into the legal framework for quarantine, at least in some places. Still, at pandemic-preparedness events, let alone during the pandemic, we saw a tendency among even seasoned public-health officials to assume that, with the correct legal powers in place, quarantine could simply be invoked, disease transmission would be successfully slowed, and we’d all move on with our lives. The problem is that quarantine has to happen in a place, to a person, over a period of time—and all of those logistics and that experience have to be planned for as well.

That said, much of quarantine’s redesign needs to happen at the federal, state, and community level, rather than being left to individuals—public health requires a public! In the book, we discuss everything from new urban-planning regulations that would ensure facilities such as stadiums and convention centers could easily switch function and serve as quarantine centers, to simple hacks that would make it easier to create spatial separation and adequate ventilation in today’s open-plan homes. But larger challenges, such as how to make sure essential workers can afford to self-isolate or how to mitigate social isolation during medical detention, demand solutions that go well beyond assembling a personal quarantine kit.

J.K.: Yours is a hopeful book, showing us how quarantines can help save us and not cause us shudders. That said, you have spent several years contemplating doomsday scenarios. What do you do for fun?

G.M.: We’re both avid hikers, and we were able to combine hiking during the coronavirus lockdown with finishing the book, doing a big loop in the Verdugo Mountains near our home in Los Angeles. We used the hikes to talk about structural issues or editorial challenges with our material, while enjoying the sun and listening to birds and even seeing a small family of deer that lived in one of the canyons off the trail.

N.T.: I can see how it might sound quite grim to be finishing a book about quarantine while in lockdown with your spouse, but, to paraphrase popular science writer Mary Roach, who was kind enough to blurb the book, quarantine is “boring to live through but unbelievably interesting to read about”—and to think and write about as well. And reporting it, pre-coronavirus, was amazing—traveling around the Mediterranean to explore ruined quarantine hospitals was an entirely delightful way to blow through our advance!

Geoff Manaugh and Nicola Twilley’s Until Proven Safe is out now from MCD, an imprint of Farrar, Straus and Giroux

Jim Kelly is the Books Editor for AIR MAIL