The name Cozumel was derived from the Mayan "Cuzamil" or "Ah Cuzamil Peten" in full, which means the island of swallows (Spanish: Isla de las Golondrinas). The island is covered with mangrove forest which has many endemic animal species. Cozumel is a flat island based on limestone, resulting in a karst topography. The highest natural point on the island is less than 15 m (49 ft) above sea level. The cenotes are deep water filled sinkholes formed by water percolating through the soft limestone soil during thousands of years. Cozumel's cenotes are restricted to qualified cave divers with appropriate credentials. The Maya are believed to have first settled Cozumel by the early part of the 1st millennium AD, and older Preclassic Olmec artifacts have been found on the island as well. The island was sacred to Ix Chel, the Maya Moon Goddess, and the temples here were a place of pilgrimage, especially by women desiring fertility. There are a number of ruins on the island, most from the Post-Classic period. The largest Maya ruins on the island were near the downtown area and have now been destroyed. Today, the largest remaining ruins are at San Gervasio, located approximately at the center of the island.