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, 122 metres (400 ft) above the sea.The casbah and the two quays form a triangle.) from the Arabic name الجزائر al-Jazā’ir, which translates as "The Islands", referring to the four islands which used to lie off the city's coast until becoming part of the mainland in 1525.Algiers is located on the Mediterranean Sea and in the north-central portion of Algeria.
The United States fought two wars (the First and Second Barbary Wars) over Algiers' attacks on shipping.
Among the notable people held for ransom was the future Spanish novelist Miguel de Cervantes, who was captive in Algiers almost five years, and who wrote two plays set in Algiers of the period.
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.
A significant number of renegades lived in Algiers at the time, Christians converted voluntarily to Islam, many fleeing the law or other problems at home.