Algiers ) is the capital and largest city of Algeria. According to the 1998 census, the population of the city proper was 1,519,570 and that of the urban agglomeration was 2,135,630. In 2009, the population was about 3,500,000. An estimate puts the population at about 5,000,000 as of 2011.Called El-Bahdja (البهجة) or alternatively Alger la Blanche ("Algiers the White") for the glistening white of its buildings as seen rising up from the sea, Algiers is situated on the west side of a bay of the Mediterranean Sea. The city name is derived (via French Alger and Catalan Alguère) from the Arabic word الجزائر al-jazā’ir, which translates as the islands, referring to the four islands which lay off the city's coast until becoming part of the mainland in 1525. Al-jazā’ir is itself a truncated form of the city's older name جزائر بني مازغان jazā’ir banī mazghannā, "the islands of (the tribe) Bani Mazghanna", used by early medieval geographers such as al-Idrisi and Yaqut al-Hamawi.The modern part of the city is built on the level ground by the seashore; the old part, the ancient city of the deys, climbs the steep hill behind the modern town and is crowned by the casbah or citadel, 400 ft above the sea. The casbah and the two quays form a triangle.