The main aim of author was to present the specific features of the architecture and urbanisation of Algiers – the capital of Algeria. The history of the city was marked by two great periods: Muslim domination (especially from the 15th century) and French colonialism (in the years 1830 – 1962). Both of these have left behind numerous traces of architectural and urbanistic thought. The material effect of French domination is the architecture of modern Algiers, which took the form of a French ville, similar to Paris, Lyon or Marseille. On the other hand, the architecture of Algiers also includes the old Arab district – Casbah, that resembles the cities of the Middle East (Madīnah in Arabic), like Istanbul, Cairo or Damascus. Both architectural traditions give the city of Algiers a cosmopolitan and universal character. The threat to the peculiar coexistence of these traditions is the progressive migration from the countryside to the city, which results in the expansion of area of slums, called bidonvilles.