And the Islamic world provided everything from coffee to books to weapons. But it wasn't just products that made their way around the eastern hemisphere thanks to the Indian Ocean. Technology spread, too. Like the magnetic compass, which is kind of crucial if you like to know where you're going, came from China. Muslim sailors popularized the astrolabe, which made it easier to navigate by the stars. And boats using sternpost rudders were easier to steer, so that technology quickly spread throughout the monsoon marketplace. The Islamic world also produced the triangular latin sail, which became super important because it allowed ships to tack against the wind.