Antsiranana Bay (also known as Diego-Suarez Bay), the large natural bay along the northeast coast of Madagascar, is considered one of the finest natural harbors in the world. The bay, protected by a narrow inlet that provides shelter from strong Indian Ocean winds, is believed to be the result of a submerging coastline or a drowned river valley that formed many peninsulas around the bay. The principal city, Antsiranana, is located on a headland; its port, formerly military, became the second commercial port of the island.