The capital city of Yemen, Sana'a is one of the oldest populated cities in the world. Historically, its strategic location has allowed it to control the movement of trading networks, governing access from the Indian Ocean and Mediterranean to the Red Sea ports. Sana'a has been a site rich in Islamic architectural history since the seventh century, when Islam was largely adopted in Yemen. Sana'a's architectural heritage is a culmination of influences and styles; containing elements of Umayyad, Rasulid, and Ottoman architecture. Particular to Sana'a is a vibrant tradition of vernacular architecture, known for its use of carved timber, stone, and stepped masonry in multi-level houses. The western city has historically been the site of palatial architecture, including the notable Ayyubid "Sultan's Garden." Other notable complexes include a number of caravanserais and public hammams. In 1974, legislation required that all new buildings be executed in accordance with the traditional Yemeni styles. In 1986, the old city was declared a UNESCO World Heritage Site. Much of the Old City has since been destroyed, as a result of bombings throughout 2015.