Anyone who has ever been irritated by honking, congested traffic, the endless sprawl, or the smoke and smog of many large cities around the globe ought to read the old Medieval philosopher Ibn Khaldun of Tunis. Six hundred years ago this renowned Islamic thinker developed some ideas on city planning that remain amazingly pertinent in the twentieth century.

Ibn Khaldun was interested, for example, in the quality of the air blowing through a city. Once while escorting a friend around Gabes in his native province in Tunis, North Africa, he remarked: "Gabes would not be habitable except for the removal of the dense palm grove that used to surround the city. Before then, the air was stagnant because it could not get past the trees.... Now that the trees are gone, the air circulates...."

The city planners of Pittsburgh may never have read what Ibn Khaldun said about Gabes. Yet they were acting on his theory when they decided to clear up the smog of the coal and steel works that used to hang heavy over the metropolis at the confluence of the Allegheny and the Monongahela rivers. The circulation of pure air revitalized modern Pittsburgh as it had revitalized Gabes during the Middle Ages. The same principle is being applied today in cities as far apart as Leeds, England, and Kuwait on the Persian Gulf.

The place of Ibn Khaldun in the annals of city planning has never matched his reputation as a historian. He is remembered primarily as a philosopher of history, in fact the founder of the subject. Before any other historian of East or West, he undertook to explain systematically the nature of civilizations and the reasons for their rise and fall. Before Montesquieu, he investigated the influence of climate on culture. Before Toynbee, he related universal religions to universal empires.

Perhaps Ibn Khaldun's most remarkable parallel is with Spengler. The late German philosopher of history took it as his fundamental thesis that cultures are like living organisms: they go through a cycle of birth, growth, equilibrium, decay and death.

Ibn Khaldun developed exactly this theory centuries ago. In the Muqaddhnah, or preface to his Universal History, he relates that the life of a city runs a course somewhat analogous to the life of a man. "Reason and tradition show that at the age of forty a human being's growth and strength die down. He ceases to develop and begins to deteriorate. Just so is it with civilized culture, because the natural limit cannot be passed without revealing its effects. The limit varies more widely with cities than with men, but the principle is the same."

Pursuing this idea, Ibn Khaldun was led to the study of cities, perhaps the most significant product of civilized life. He traveled widely in the Islamic world of his time, inspecting every kind of settlement from hamlet to metropolis. He brought back voluminous notes on the splendid cities he visited—Tunis, Cairo, Damascus, Baghdad, Cordova, Seville. He made the pilgrimage to Mecca and paused along the way to gather on-the-spot information about life in the desert villages.

When he sat down in his study to write his great work, the Muqaddimah, he knew that much of it must be devoted to city planning. This is the part of his book that seems so up-to-date today.

Ibn Khaldun argues that no city can endure indefinitely at the high-tide of its prosperity. The longer the city lasts, the higher its development, the less active its population becomes. Idleness and corruption grow. Luxuries change into necessities. Money takes on an increasing importance, and, paradoxically, has less value.

Those who think that inflation is a modern discovery should consider this sentence from the Muqaddimah: "A city with a large population develops a competition for goods, and the result is rising prices in the bazaars." Ibn Khaldun concludes, as might any contemporary economist, that "the financial stability of the city begins to deteriorate, with a concomitant deterioration in the body politic."

This pathology of cities is obviously relevant to Ibn Khaldun's philosophy of history. So, conversely is the health of cities.

Following Aristotle's ideas, he explains that cities are a very necessary part of civilized life. Since human beings prefer to live together in groups, it follows that their habitations must be located together. And therefore some cities will arise spontaneously, if they are not deliberately constructed.

Nothing about the city, according to Ibn Khaldun, is of greater concern than its site, the physical layout of its location. If the City is of spontaneous origin, the site is likely to be a good one, for people will not willingly gather where living conditions are bad. On the other hand, the layout of streets and buildings may well be poor, dictated by chance, necessity and individual whim instead of a rational planning authority. Damascus is mentioned as a case in point for Ibn Khaldun—so well situated that it was inhabited from the earliest times, yet it is full of narrow, winding streets and back alleys.

The city deliberately founded and encouraged to grow by one man usually is well constructed internally, like Baghdad with its geometrical divisions and broad, handsome boulevards. But Baghdad's excellent position on the Tigris is not emulated in all "artificial" cities. Too often the founder seeks only a few good conditions and ignores the rest. "Thus, those who founded some of the towns in the Hijaz concentrated on pasture and water suitable for their camels. They overlooked food and water for themselves, and for their other domesticated animals like cattle, sheep and goats."

Building material is another problem over which city planners have sometimes faltered. Ibn Khaldun criticizes his compatriots for working too much with wood and adobe, suggesting that they import stone and marble—the endurance of which would be worth the extra cost. As proof he mentions the Pyramids.

The correct administration of any city calls for proper zoning, a problem that plagues many a twentieth-century city. Ibn Khaldun's argument implies that faulty spacing, the intermingling of different districts—residential, industrial, financial, recreational—is an invitation to chaos. The main thing, he says, is to have order in zoning so that each element in the life of the city may enjoy the conditions most appropriate to it. Under this heading, he explicitly notes that parks should be spaced at intervals for the benefit of the entire population.

Ibn Khaldun has a long section on the arts and crafts of the city. Earlier than Adam Smith, he realized the significance of the division of labor—the fact that in urban life no individual can produce everything he wants, so that some citizens confine themselves to carpentry, others to medicine, others to trade, until all the needs of the citizens are met.

Commerce, too, has a special place in Ibn Khaldun's analysis of cities. Commerce, he states, caters to goods that cannot be manufactured locally, and however much the Islamic philosopher of history might deplore the emphasis on luxury, he was realistic enough to write this: "The residents of Damascus could do without Chinese porcelain or Indian spices, but wealthy Damascenes will not do without them, now that they are to be found in the bazaars."

Ibn Khaldun does not forget the arts that are non-productive in the ordinary sense. They do not produce food, clothing, or housing. Nevertheless, he exhorts city governments to support poets, musicians, painters, writers and book publishers. He suggests, moreover, that cities encourage science by founding scientific schools and institutes. His opinion here refers not only to such studies as law and theology, but also the practical training of apprentices in metalwork and cloth dyeing.

The startling modernity of Ibn Khaldun's thought means that he has words of wisdom for city planners of every time and place. His broad theories are still correct, his practical solutions still applicable. Above all, Ibn Khaldun of Tunis wanted cities that were good to live in.