Diamond Head is a volcanic tuff cone crater to the south-east of Honolulu, Hawaii. It was originally named Laeahi by the ancient Hawaiians. The name meant "brow of the tuna" and looking at the silhouette of the crater from Waikiki, you can see the resemblance. The current name came was given to the crater by British sailors in the 1800's. When they first saw the crater at a great distance, the calcite crystals in the lava rock appeared to glimmer in the sunlight. The sailors mistakenly thought there must be diamonds in the soil. Diamond Head is a crater that has been extinct for 150,000 years. The crater is 3,520 feet in diameter with a 760-foot summit. When the United States annexed Hawaii in 1898, harbor defense became a main responsibility. One of the major defense forts, Fort Ruger, occupied the Diamond Head Crater.