How did the printing press spread across Europe so fast?

It spread fast because demand was huge, the secret got out, and the machine could travel. Around 1440, the goldsmith Johannes Gutenberg in Mainz built a press with movable type. At first his shop was the only one in Europe. By the end of the 15th century, about 270 European cities had printers.

The demand was there before the press. Copying books by hand was slow and expensive, and there were far fewer manuscripts than readers wanted. Then Gutenberg lost a lawsuit to his investor, Johann Fust, who took over the shop. With Gutenberg's monopoly gone and the technique no longer secret, German printers emigrated and trained foreign apprentices, and presses popped up in Cologne, Rome, Venice, Paris and London within about two decades.

The equipment was portable, too. When a bishop or a prince tried to shut printing down in one city, the printers simply moved next door. And the Latin alphabet helped: a few dozen letters are far easier to cast than the thousands of characters Chinese printers needed, even though China had invented movable type centuries earlier.

The results were staggering. European presses turned out over 20 million copies by 1500. Within three years, printers distributed 300,000 copies of Martin Luther's writings, surprising the pope and rulers alike. One invention, one lost lawsuit, and the way ideas travelled changed for good.