British sailors mistook sparkling calcite crystals here for diamonds in 1825, giving this ancient volcanic cone the name you know today. To the ancient Hawaiians, this crater was known as Le'ahi, which translates roughly as 'brow of the tuna fish,' a reference to the shape of the ridgeline when seen from the sea. A heiau — a Hawaiian sacred platform — once stood on the summit, used for human sacrifice in the religious practices of the ali'i.
The English name came from a misidentification: when British sailors landed in 1825, they spotted calcite crystals sparkling in the rock and thought they had found diamonds. They were wrong about the minerals, but the name stuck. The military use of Diamond Head began during the First World War, when the U.S. Army built a network of tunnels, gun batteries, and observation stations inside the crater to defend Honolulu.
Fire Control Station One, completed in 1910, gave the Army a commanding view of the entire southern coast of O'ahu. Today, the 0.8-mile trail to the summit is one of the most popular hikes in the world, rewarding those who make the climb with a 360-degree panorama of Honolulu, the Ko'olau Range, and the vast Pacific beyond.