City walls conquered the ancient world and then disappeared. Why?

Ancient cities — the kind we know of more through archaeology than written history — tend to have a bunch of features that set them apart from smaller, less ambitious settlements. Most of these are still familiar, in some form, and not just in your friendly local metropolis. Look around any small town today, and you’ll spot the contemporary equivalents of monumental public buildings (town halls and civic centers), granaries (supermarkets), and temples (churches, mosques, and, well, temples).

There is, however, one feature common to most ancient cities that you’ll find surprisingly hard to locate now: For huge swathes of human history, almost any city worth its salt would be at least partially surrounded by walls. Nor were the aforementioned swathes restricted purely to ancient history. Paris built its last defensive wall, the 21-mile (33km) Thiers Wall, as late as the 1840s, and if you’ve ever taken the city’s trams 3a or 3b, you’ve traced its former path around the Boulevards des Maréchaux. Copenhagen built its last fortifications, the 19-mile (14km) Vestvolden — western rampart — nearly half a century after even that.

By then, though, such things were rarities. And the most famous urban wall of modern times — which surrounded West Berlin between 1961 and 1989, built by those who lived outside it, in a strange attempt to stop themselves from getting in — is not generally regarded as a good thing. From Carcassonne to Chester, Dubrovnik to Beijing, there are many cities where you’ll still find walls today. But these are tourist attractions precisely because they’re picturesque historic sites, not still active parts of city life. Something has changed.

The earliest settlement at Jericho, in what’s now the West Bank, dates from around 9000 BC. Its first set of walls — perhaps 12–15 feet (4m) high and 6 feet (2m) thick, and equipped with a 28-foot-tall (8m) defensive tower; a complex that would have taken enormous communal effort to construct — dates from perhaps a thousand years after that. That puts the earliest known walls — built, it’s assumed, to protect the people and resources inside them from outsiders — as far back from the golden age of the first city, Uruk, as that time was from us. Little wonder that, when the writers of the Old Testament wanted to suggest God was on the Israelites’ side, it was the walls of Jericho that the trumpets brought tumbling down.

As prehistory turned to history and settlements dwarfing Jericho began popping up all over the place, walls became not merely a must-have for a city, but a veritable symbol of what it was to be one. Inscriptions in Uruk credit the historic version of the legendary hero-king Gilgamesh with building the city’s walls, probably sometime around 2800 BC. In the comparatively recent times of the 6th century BC, the dynasty of Nebuchadnezzar rebuilt and expanded the walls of Babylon, and created a new processional way ending in the grand blue Ishtar Gate to finish the job. In the metropolis of the ancient world, walls stood as a mark of the power a king had to direct labor and reshape the very world he ruled over. They didn’t just symbolize the city: They symbolized civilization itself.

Not that the two were necessarily, at this stage, different.

That’s not to say that every city had walls. Sparta did without them until the 2nd century BC, a good 250 years after the peak of its power: the defensive strategy of “a bunch of soldiers, universally agreed to be bloody terrifying” turned out to be quite barrier enough. At the far end of Eurasia, many Southeast Asian cities didn’t bother with such things until the edge of modern times, when Europeans started showing up in boats. Tragically, but unsurprisingly, this seems to be less a matter of learning from superior Western technology than realizing this would be a good time to start locking up their stuff.

Nor did all the many defenses that did exist necessarily look the same. The walls you’ve been imagining are probably the sort you’re most likely to still encounter today: masonry structures with battlements, towers or bastions. But survivorship bias is likely a factor here — thick stone walls are simply more likely to survive the millennia — and plenty of settlements instead favored ditches or earthworks, spiked wooden palisades or structures of brick. Many used impassable features of the landscape — rivers and coastlines, mountains and cliffs — to save on stone and labor.

The cities of China, meanwhile, often used rammed earth surrounded by a protective layer of stone, a combination that’s a damn sight tougher than it sounds. So immense could Chinese walls be that those of the marketplace of occasional capital Chang’an are reported to have been thicker than those of many European capitals; so tough were they that, even though the Chinese invented gunpowder, the East may have fallen behind the West in artillery technology in large part because it seemed completely implausible that any cannon could ever be strong enough to break such walls.

The greatest walls were, unsurprisingly, those found in the grand imperial centers. In 762, when the Abbasid caliph al-Manșūr decided to build a new capital for his Islamic Empire just down the road from Babylon, he decreed that it should be surrounded by three sets of perfectly circular walls. The defenses of the Round City — you know it as Baghdad — were reportedly 4 miles in circumference and up to 80 feet high. A thousand miles away, the eastern Roman capital of Constantinople — today’s Istanbul — was built on a peninsula and so successfully defended that it survived sieges by the Persians, Arabs, Bulgars and Rus, among others, and outlasted the western empire by nearly a thousand years. Even when it finally fell in 1453, the invading Ottomans never breached the walls: It was simply that those inside them decided that, on balance, they’d rather have something to eat.

But a city didn’t need an empire to have a good wall. Medieval England had hundreds of walled towns, some dating from the Roman era, others from the 9th century, when Alfred the Great ordered fortified “burghs” be built to defend the inhabitants from Viking invaders. Even in the New World, early European settlements — Boston, Halifax, Montreal — commonly came with walls. There is a reason New York City has a Wall Street.

The fact that cities of vastly different sizes and status all bothered with such things is a reminder that walls could serve mul­tiple purposes. Their most obvious function was defensive — a way of protecting the inhabitants and their stuff from falling to any passing horde that fancied a spot of marauding. This, of course, is why so many wars involved sieges, in which citizens would hunker down behind their walls, while invaders would attempt to breach them using some combination of ballistic weapons, battering rams and siege towers — huge, mobile platforms giving attackers both somewhere to hide and an elevated position from which to fire down or climb over. Particularly unpleasant be­siegers could also employ primitive forms of biological warfare, chucking plague-ridden corpses over the walls, in the hope of persuading the inhabitants that there were worse outcomes here than opening the gates.

Walls also performed other functions that weren’t defensive. Forcing all farmers and merchants through particular gates allowed city authorities to regulate trade and tax goods going in and out. And like monuments or grand buildings, they could also act as a marker of the status and independence of a city, a visible symbol of civic pride: The lords have their castles, they said, but we, as a community, have this. When invading armies aimed to destroy town walls, it was often about their symbolic function as much as their defensive one. Not for nothing does the Epic of Gilgamesh both begin with a paean of praise to walls “which gleam like copper” and end with him showing them off to an outsider, Urshanabi the ferryman.

By the time modernity arrived, what had once been a near-universal feature of urban life had either turned from vital civic architecture to cutesy historic artifact, or had vanished completely.

Even during the heyday of city wall building, they often didn’t surround everything required for urban life. The so-called noxious trades — slaughterhouses, tanneries, those involving waste — often remained outside the city for reasons of health risk or stinking like hell. The poorest residents, too, were sometimes stuck in suburbs where they’d have fewer defenses but where land was cheaper, while the relative lack of regulation meant that nightlife — taverns and theaters, brothels and bear-baiting — often also lay outside. It’s no coincidence that William Shakespeare plied his trade outside the City of London proper, in extramural Shoreditch or transpontine Southwark.

That city’s walls had stood, in varying states of repair, since Roman times — but within a few decades of Hamlet treading the boards, “London” would cease to refer primarily to the area within them. The population, already booming in the 16th century, would explode in the 17th, forcing unprecedented levels of building outside the ancient walls; from the 18th, they’d be torn down. Today, all that’s left are a few stretches of ruins, and a bunch of street names or tube stations with “-gate” as a suffix. Though the timescales would vary from place to place, that was pretty much the pattern. By the time modernity arrived, what had once been a near-universal feature of urban life had either turned from vital civic architecture to cutesy historic artifact, or had vanished completely.

Partly this was down to advances — that may not be the right word, but let’s go with it — in military technology. Once gunpowder had been invented and cannons reached a certain strength, a mere stone wall was not necessarily enough to hold back an army. By 1871, in one of those historical ironies so perfect you wonder if somebody is doing it deliberately, Adolphe Thiers — the man for whose premiership the last walls of Paris had been named — was president of the Third French Republic. That year, to crush the upstart revolutionary government of the Paris Commune, he ordered his troops to bombard the city. The walls he’d proposed three decades earlier protected it not a jot.

But the other reason walls fell out of favor is the one London’s history hints at. Both industrialization and the transportation revolution that accompanied it meant that cities became much, much bigger, and their residents vastly more spread out. By the end of the 19th century, most settlements of any significance were simply far too big to be bounded by masonry and brick.

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