Cities & civilization

What turns villages into something larger is a simple sum. If a farming family grows only what it eats, everyone must farm. On rich, well-watered soil, though, a family can grow more than it needs. The extra is a surplus, and every city stands on one.

A surplus can feed people who grow nothing. It frees a potter to make pots all day, a smith to work metal and a scribe to keep accounts, and each becomes better at the one job than a part-time farmer ever could. Such a full-time worker at one trade is a specialist. The numbers stayed lopsided for a very long time: in the farming societies of the ancient world, roughly nine people in ten still worked the land, and only a thin slice lived off the surplus. City life begins in that thin slice.

The surplus was largest where rivers watered flat, fertile land. One such place was Mesopotamia, the plain between the Tigris and the Euphrates in what is now Iraq, and there villages grew into the first cities. The best known is Uruk. By about 3100 BC it held tens of thousands of people, and not long after 2900 BC it was ringed by a mud-brick wall nine kilometres long.

Uruk’s temples took in grain, sheep and cloth and handed them out again, and no memory could keep track of it all. So their accountants pressed marks into wet clay: so many measures of barley, received over so many months. Those tablets are among the oldest writing ever found, and it began as bookkeeping. Another early tablet lists more than a hundred job titles, the specialists a surplus had made room for.

Pack tens of thousands of people inside one wall and problems appear that no village has. Water must reach every quarter, and waste must leave it. Grain has to come in from the fields and be stored against a bad year. Streets have to let carts and crowds pass, and the wall itself needs gates and repair.

None of this can be done household by household. It takes shared built works that serve everyone at once: canals and wells, drains, roads, storehouses, walls. Together they are a city’s infrastructure. Mesopotamia’s cities lived by their canals, which carried river water to the fields and barley back to town, and when a river shifted its bed and left the canals dry, the city they fed declined. A city is its people, but it lasts only as long as the works that carry them.

A city is crowded and has to be fed from outside. Why would anyone choose it? Ibn Khaldūn, a North African scholar and judge who wrote his great book on society, the Muqaddimah, in 1377, began his answer with a loaf of bread. No one, he wrote, can get even his daily wheat alone. It must be ground, kneaded and baked, and each step needs tools that only a blacksmith, a carpenter or a potter can make.

Splitting work up like this, each person keeping to one trade and trading for the rest, is the division of labour. People who cooperate, he observed, produce far more than they need themselves, enough to supply many times their own number. The more people a city holds, the more labour is left over once its needs are met, which is why he found big cities richer than small ones.

Cities do not arrive alone. Where they appear, a cluster of other things tends to appear with them: full-time specialists, writing, a government, and great buildings such as temples. Each such monument takes labour that only a surplus can spare. Historians call the whole bundle civilization, a word built on the Latin for citizen, the member of a city. No single piece makes it. A village with one scribe is still a village.

Ibn Khaldūn had his own word. He called it umran, from an Arabic root that means to build up and to cultivate, and he used it for all organised human society, from a desert camp to a great capital. He believed nobody before him had studied it as a subject in its own right. So he announced a new science, the science of umran, to explain how societies form, grow rich and come apart.

Thousands of strangers living side by side will quarrel over boundaries, debts and water, and a city cannot settle every quarrel by feud. It also has canals to dig, walls to man and a surplus to collect and store. All of that calls for a lasting authority with the power to command, judge and tax. That organised power is the state. It is more than its ruler: kings die, and the offices, courts and tax rolls carry on under the next one.

A state can use force, but no state has enough soldiers to stand over every household. Rule lasts when most people accept it as rightful and obey without being made to. That acceptance is called legitimacy. Ibn Khaldūn put the need plainly. People who live together, he wrote, need someone with authority to restrain them from harming one another.

Walk into the old quarter of Fez, Tunis or Aleppo and the plan repeats. Near the middle stands the congregational mosque, the one large enough to hold the city’s men for the Friday prayer. Announcements were made there, judges often sat there, and scholars taught in circles against its pillars.

Pressed up against it is the market, in Arabic the sūq: lanes of shops grouped by trade, the booksellers and perfumers nearest the mosque, the noisy and smelly crafts such as tanning out towards the walls. From the eleventh century a third building spread from city to city and joined them, the madrasa, a college where students lodged and studied law and the religious sciences, paid for by a charitable endowment. Prayer, trade and learning sat within a short walk of one another, and the houses spread outward from there.

Some cities grow slowly from a market or a river crossing. Others are ordered into being. In 762 the Abbasid caliph al-Manṣūr had a new capital laid out beside the Tigris as a circle, with his palace and the main mosque at its centre and four gates in its walls. He named it the City of Peace. We call it Baghdad, and within a few generations it was among the largest cities on earth.

Other dynasties built or remade capitals of their own. The Idrisids founded Fez in 789. The Umayyads of Spain made Cordoba the seat of a caliphate in 929. The Fatimids laid out Cairo in 969. Ibn Khaldūn made it a rule. Dynasties come before cities, he wrote, because only a ruler can command the labour of many workers and find the pay that such building needs.

So who founds dynasties? Ibn Khaldūn’s answer began far from any city. He compared two ways of living. One is the hard life of the desert, by which he meant all the open land beyond the towns, where herders and small farmers own little and have no walls and no garrison to protect them. The other is the settled life of towns, with its markets, crafts and comforts.

In the desert, he argued, a family stays alive only because its own kin are defending it, so the bond between them grows fierce. He called that bond asabiyya, group feeling: the loyalty that makes the members of a group act as one and risk their lives for each other. Townspeople have walls and a governor’s soldiers to do their fighting. They need the bond less, and it slackens. The rest of his theory follows from that one difference.

Put the pieces together and a pattern appears. A hardy group from the margins, bound tight by group feeling, can defeat a larger but looser kingdom. Its leaders take the throne and move into the palaces of the people they conquered.

Then the victory starts to work against them. The rulers and their children take to fine food, fine clothes and grand buildings, and Ibn Khaldūn’s word for all of it is luxury. Luxury costs money, so taxes rise. It also softens. Sons raised in palaces have never needed their kin to stay alive, and the group feeling that won the kingdom weakens with each generation. The decline ends with a court that spends more than it takes in, quarrels with its own kin and is defended by hired soldiers. Out on the margins another hardy group is waiting, and the cycle begins again.

How long does the slide take? Ibn Khaldūn gave a number. A dynasty, he wrote, seldom lasts beyond three generations, and he counted a generation as forty years: about a hundred and twenty years in all.

In another chapter he sketched the generations of a great house one by one. The first is the builder. It lived the hard life, won the kingdom and knows what that cost. The second knew the builder in person and keeps most of his ways, though learning by watching is weaker than learning by doing. The third knows the struggle only as a family story and relies on tradition without understanding it. If a fourth follows, it is the destroyer. Born to rank, it takes obedience for its birthright, looks down on the people whose loyalty holds it up, and loses everything.

Ibn Khaldūn did not blame a dynasty’s fall on its last, weakest king. A dynasty, he wrote, has a natural life span, like the life of a person. It grows, matures and in old age weakens from causes built into it, and he called that old age a sickness no ruler can cure. He saw these regular causes as the way God deals with His creatures.

He found limits in space too. A conquering group has only so many men, and every province it takes needs some of them as a garrison. He compared a dynasty’s power to rays of light spreading from their source, strongest at the centre and faint at the edge. Historians now call reaching past what a state can hold overextension, and the borders are the first thing it costs. Explaining events by causes that repeat is what makes his book a work of science.