Algiers is the capital and largest city of Algeria. In 2011, the city's population was estimated to be around 3,500,000. An estimate puts the population of the larger metropolitan city to be around 5,000,000. Algiers is located on the Mediterranean Sea and in the north-central portion of Algeria. Sometimes nicknamed El-Behdja or alternatively Alger la Blanche 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 modern part of the city is built on the level ground by the seashore; the old part, the ancient city of the days, climbs the steep hill behind the modern town and is crowned by the casbah or citadel, 122 metres above the sea. The casbah and the two quays form a triangle.