Humankind's greatest creation has always been its cities. They represent the ultimate handiwork of our imagination as a species, compressing and unleashing the creative urges of humanity. From the earliest beginnings, when only a tiny fraction of humans lived in cities, they have been the places that generated most of mankind's art, religion, culture, commerce, and technology.

Although many often mistakenly see cities as largely a Western phenomenon, with one set of roots, urbanism has worn many different guises. Over the past five to seven millennia, cities have been built in virtually every part of the world from the highlands of Peru to the tip of southern Africa and the coasts of Australia. Some cities started as little more than overgrown villages that, over time, developed momentum and mass. Others have reflected the conscious vision of a high priest, ruler, or business elite, following a general plan to fulfill some greater divine, political, or economic purpose.

The oldest permanent urban footprints are believed to be in Mesopotamia, the land between the Tigris and Euphrates River. From those roots sprang a plethora of metropolises that represent the founding experiences of the Western urban heritage, including Ur, Agade, Babylon, Nineveh, Memphis, Knossos, and Tyre. But many other cities sprang up largely independent of these early Mesopotamian and Mediterranean settlements. Some of these, such as Mohenjo-daro and Harrapa in India and Chang'an in China, achieved a scale and complexity equal to any of their Western contemporaries. All of these cities, numerous and various, are however reflective of some greater universal human aspiration.

The key to understanding that universal aspiration lies in the words of the Greek historian Herodotus. While traveling in the 5th century B.C. to places both thriving and struggling, he wrote, "For most of those which were great once are small today; and those that used to be small were great in my own time." Cities throughout history have risen and fallen. The critical questions of Herodotus' time still remain: what makes cities great, and what leads to their gradual demise?

I argue that three critical factors have determined the overall health of cities: the sacredness of place, the ability to provide security and project power, and the animating role of commerce. Where these factors are present, urban culture flourishes. When these elements weaken, cities dissipate and eventually recede out of history.

The Sacredness of Place

Religious structures