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.
The nobah or nawbah of Yemen are cylindrical tower farmhouses that serve as residences and as fortresses. They are the descendants of pre-Islamic and early-Islamic circular stone structures of the region. These farmhouses can be found throughout the province of Sana'a, some having been integrated into the city as it expanded. Some nobah constructed in ashlar masonry still stand as part of palaces of the Imam that ruled the city.
With their cylindrical form, the nobah are structurally very strong. Some even support the popular mafraj, a rectangular parlor for receiving and entertaining visitors at the top story of the house. Like the non-cylindrical tower houses, the first floor of the nobah is reserved for storage. The family living quarters are located above the storage areas.
Lewcock, Ronald, Paolo Costa, R.B. Serjeant, and Robert Wilson. "The Houses of San'a'." In San'a an Arabian Islamic City, edited by R.B. Serjeant and Ronald Lewcock, 464-465, 468, 485, 488. London: The World of Islam Festival Trust, 1983.
Lewcock, Ronald, R.B. Serjeant, and G. Rex Smith. "The Smaller Mosques in San'a." In San'a': An Arabian Islamic City, edited by R.B. Serjeant and Ronald Lewcock, 386. London: The World of Islam Festival Trust, 1983.
Lewcock, Ronald, Paolo Costa, R.B. Serjeant, and Robert Wilson. "The Urban Development of San'a'." In San'a an Arabian Islamic City, edited by R.B. Serjeant and Ronald Lewcock, 123-138. London: The World of Islam Festival Trust, 1983.