Today, a 2200-year-old age of invention. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Alexander the Great fell ill and died in 323 BC. He was only 33. As a teenager he'd studied with Aristotle. From the age of 16 to 20 he'd been the general who helped his father Philip II unify Greece. Then Philip was assassinated, and the armies made Alexander their king. Over the next 13 years, Alexander had conquered present-day Egypt, the Holy Land, Turkey, and a swath eastward from there all the way to Pakistan.

But these had been no ordinary conquests. Those years with Aristotle had made a scientist of Alexander. He extracted knowledge from foreign lands and stirred Greek culture into theirs. He worked very hard at mixing the cultures of East and West -- at stimulating trade, cultural exchange, and intermarriage.

His empire fell apart after he died, but the effects of it were lasting. Of fifteen cities he'd founded and named Alexandria, the one northwest of Cairo emerged as the center of Mediterranean culture. A new dialect of Greek, the Koinia, became the common language of the Eastern Mediterranean basin. The closed world of the Hellenic city-states gave way to polycultural Hellenistic civilization.

Alexandria drew talent like a magnet. Euclid, Archimedes, and the astronomer Ptolemy all worked there. The astronomer Eratosthenes accurately calculated Earth's diameter. Alexandria remained the intellectual center of the world for three centuries -- until Octavian claimed Egypt for Rome after Cleopatra's suicide in 30 BC.

The much-praised technology of the Romans was built on inventions of the great Alexandrian engineers. Plumbing, gearing, and water wheels all came from Alexandria. Those Greco-African engineers had names -- like Ktsebios, Philon, and Heron (or Hero).

The most remarkable Alexandrian invention was feedback control. A feedback device automatically corrects the way a machine functions -- like our thermostats, speed controllers and pressure regulators. The Alexandrian engineers invented all sorts of float valves and other liquid-level regulators. The most important machine that used these gadgets was the water clock. The Alexandrian water clock was the basic time-keeper until the mechanical clock replaced it around AD 1300.

Alexandria was free-wheeling, open, cosmopolitan, and wonderfully inventive. After the authoritarian Romans moved in, invention withered in Alexandria. And no new use was made of feedback until a new craving for freedom swept Europe in the middle of the 18th century. But let's leave that for another day.

Other intensely creative civilizations have surfaced throughout history -- the Court of Baghdad, the High Middle Ages, nineteenth-century America. All those epochs reinforce one inescapable message about powerful creativity. They all show us what free people, exposed to wide-ranging outside influence, can do when they let their minds run free.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Clough, S., A History of the Western World, Vol. I, Ancient Times to 1725. Boston: D. C. Heath, 1964.

Mayr, O., The Origins of Feedback Control. Cambridge, MA: MIT Press, 1970.

See also various encyclopedia articles on Alexander the Great.

This is a greatly revised version of Episode 53.

Egypt as portrayed in the 1897 Encyclopaedia Britannica.
Alexandria (upper left) looks out over the Mediterranian
While Cairo (lower center) is situated deep within Egypt.