Algiers is the capital and largest city of Algeria. The city’s name is derived from its location on the slopes of the "Sahel", a chain of hills parallel to the coast. Algiers is located on the Mediterranean Sea, in the north-central part of the country, in from a cluster of islets that now have been turned into a part of the port.

The modern part of the city is built on the level ground by the seashore and the old part, the ancient city, climbs the steep hill behind the modern town and is crowned by the kasbah or citadel, 400 feet above the sea.

Algiers is the country's main harbor, serving both as a shipping center and a principal Mediterranean refueling station. Algiers has the best connections to other urban centers in the country with a number of highways and roads running out of it, as well as a southern and an eastern-bound railway. The main industries in the city are oil refining, petrochemicals, metal working and foodstuffs.

The city is divided into three parts: the lower part, the French areas, which were erected after the demolition of the traditional quarters, when the French put up their new administrative centre; the upper part which is known as the kasbah, and has over the recent decades turned into almost a slum; and the third part which is made up of the large suburbs surrounding the city, which date to the post-colonial period. These suburbs now cover most of the surrounding Metidja plain.

Founded in 1200 BC by Phoenicians, Algiers was first a trading post called "Icosium". In myths, Icosium is thought to have been established by 20 friends of the legendary hero Hercules. After the Phoenicians, Algiers (Icosium) was maintained during the Carthaginian era, and it later became part of the Roman empire in 146 BC. Demolished in the 400s by the Vandals, Algiers then became part of the Byzantine empire in 146 BC. It was controlled by the Arabs in 650 and as part of the Berber dynasty the 900s became a focal point for Mediterranean trade.

Algiers then became a sanctuary for the Moors, who had been banished from Spain in the 1500s. Many of these expelled Moors turned to piracy and attacked European, especially Spanish, trading ships, making Algiers a pirate stronghold along the "Barbary (pirate) coast". In retaliation, Spain took over many ports along the Barbary coast that were known to be centers for piracy and changed them into Spanish forts. The Muslim people of Algiers turned to the two Turkish pirates, 'Barabossa' and his brother Andruj, to drive the Spaniards away from Algiers.

Andruj and Khayr ad-Din, helped to expel the Spanish presence from Algiers. Khayr ad-Din ultimately gained control of Algiers for the Ottoman sultan Khalif in 1529 using the support of the Ottoman empire and his own pirate navy. Prior to fighting on behalf of the Ottoman empire, he and his brother had planned to gain control in North Africa by making alliances with the Turks and the Muslims who had been expelled from Spain. When his brother Aruj was killed by the Spanish in 1518 during the battle at Tlemcen, Khayr ad-Din appealed to the Ottoman sultan Khalif for help. He was named a beylerbey, the sultan's representative in Algiers, and given military aid by the Ottoman sultan in 1518.

Algiers remained a pirate stronghold for 300 years, an important part of the Ottoman empire and a bulwark against the Spanish imperialism. Algiers resisted Europe's continual efforts to halt the piracy, which plundered European trading ships, hurting the European economies, until finally on July 5, 1830, it fell to the French. As the base of France's North African colonies, Algiers once again held significance as it entered the colonial period, this time as a powerful colony.

In 1962, after a bloody independence struggle in which hundreds of thousands of Algerians died at the hands of the French army and the Algerian Front de Libération Nationale, Algeria finally gained its independence, with Algiers as its capital.

Reference: 

lexicorient.com/e.o/algiers.htm

en.wikipedia.org/wiki/Algiers 

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