Ferdinand Magellan was a Portuguese sailor who couldnโt get his own king to fund a daring plan: sail west to reach the spice-rich islands of Asia. So he switched sides and convinced the king of Spain instead. In 1519 he set sail with five ships and about 270 men.
The journey was brutal. They fought off mutinies, got stuck in a freezing strait at the bottom of South America (now called the Strait of Magellan), and then sailed for 99 days across a giant unknown ocean without spotting any land. Men starved and chewed leather just to survive.
Magellan himself never made it home - he was killed in a battle in the Philippines in 1521. But one battered ship, the Victoria, limped back to Spain in 1522 with just 18 starving survivors. They had circled the entire planet, proving for certain that Earth is round.