Precedentthe patterns history keeps Start the walk →
Entry 76 of 240Invention

Ptolemy's Almagest

c. 150 CE/Egypt/Roman Egypt
Today Alexandria, EgyptSpan Roman Egypt · 30 BCE – 641 CE

Working in Alexandria, Ptolemy compiled a mathematical model of the heavens that put Earth at the centre and explained the planets' looping motions with circles turning on circles. It was wrong, and it worked — accurate enough to predict positions for centuries, which is why it went unchallenged for 1,400 years, translated into Arabic as the Almagest and taught from Baghdad to Oxford. His geography, with its coordinates and its badly undersized Earth, was still being consulted by navigators in the 1490s.

◆ Worth knowingPtolemy's map underestimated the planet's size, and Columbus used numbers descended from it to argue Asia lay a short sail west. He was wrong, sailed anyway, and hit a continent Ptolemy never knew existed.
◆ The mechanismInformation-medium revolution

A new way to record or transmit information lowers the cost of copying ideas and reorders who holds knowledge and power.

Also: Ideological movement · Trade-route shift

This is one stop on a walk through the whole human story, in order.

Precedent runs from 9500 BCE to the present in 240 short entries, a few a day. Under each one is the mechanism it's an instance of, and every earlier time you've walked past it. Free, no account needed.

Begin at 9500 BCE → Already walking? Open Precedent and you'll pick up where you left off.