Density was discovered by a Greek mathematician named Archimedes. He was born in the city of Syracuse, which was the heart of art, commerce and science, and his father, Phidias, was a mathematician and an astronomer. Archimedes traveled to Egypt to study in Alexandria, which had a great reputation of scholarship and learning, and he later returned to Syracuse to focus on his ideas.
At around 250 B.C., Hiero II, King of Syracuse, tasked Archimedes with determining whether his crown was made of pure gold. The king was suspicious that the craftsman who made the crown defrauded him. This challenging task put Archimedes' reputation on the line. He often went to the public marketplace to discuss scientific questions, but for this task, he chose to stay at home.
Instead, Archimedes decided to relax in a bathtub to think about the problem. He filled the tub to the brim, and as he immersed himself in the water, he observed that the water spilled over the sides. This triggered an idea that could help him handle the king's task. He realized that the volume of water that had spilled was equal to the space occupied by his body.
This fact gave him a method of differentiating between a pure gold crown and a mixed crown. Because silver occupies more space than an equivalent measure of gold, he decided to immerse the crown in water. When he submerged the crown, more water spilled over the sides. Archimedes concluded that the crown was not pure gold and that the craftsman defrauded the king. This historical event explains how he discovered density.