Algiers, in Tamazight Dzayer and in Arabic al-Jaza'ir, is the capital and largest city of Algeria, set on the Bay of Algiers between the Mitidja plain and the Sahel hills. The Roman foundation Icosium preceded the medieval Berber city; the modern toponym derives from the Berber-Arabic al-Jaza'ir Bani Mazghana, "the islands of the Banu Mazghanna," after the Sanhaja tribe that controlled the bay in the tenth century.
The city was refounded around 944 by the Sanhaja prince Buluggin ibn Ziri as a coastal fortification of the Zirid dynasty. It rose to political prominence under the Ottoman regency from 1525, when the corsair commander Khair ed-Din Barbarossa established Algiers as the seat of the Beylik of Algiers, a near-autonomous Ottoman province whose privateering economy and political institutions structured the western Mediterranean for three centuries.
The French conquest of 5 July 1830 ended the regency and inaugurated 132 years of colonial rule. The Casbah of Algiers — the medieval-and-Ottoman walled city above the modern port — was the principal site of the urban guerrilla phase of the Algerian War (Battle of Algiers, 1956–57), and is the conventional dateline of late twentieth-century anti-colonial warfare in cinema and political memory. The Casbah was inscribed by UNESCO in 1992.
The contemporary Algiers metropolitan area extends across the Mitidja and Sahel and houses approximately three million people, drawn from across Algeria and historically including substantial Kabyle, Mozabite, and Chaoui populations alongside the broader Algerian-Arabophone majority. Tamazight is widely spoken as a household language by these communities; the public administrative language of the city is Arabic with French as a continuing technical and commercial register.