The Avenue Circulaire, which surrounds the observatory built in 1883, was at the end of the 19th century mainly a resort neighborhood with quite affluent villas. Urbanization resumed after the Première Guerre World War to intensify in the '50s. We will thus discover the house of the director of the observatory, of academic style inspired by Italian classicism, an Art Nouveau school, a magnificent modernist telephone exchange completely glazed as well as several houses thus including the primer of the architectural styles of the 20th century.