In May 1968, protesting students occupied the Sorbonne and put up barricades in the Latin Quarter. Thousands of Parisian blue-collar workers joined the students, and the movement grew into a two-week general strike. Supporters of the government won the June elections by a large majority. The May 1968 events in France resulted in the break-up of the University of Paris into 13 independent campuses. In 1975, the National Assembly changed the status of Paris to that of other French cities and, on 25 March 1977, Jacques Chirac became the first elected mayor of Paris since 1793. The Tour Maine-Montparnasse, the tallest building in the city at 57 storeys and  high, was built between 1969 and 1973. It was highly controversial, and it remains the only building in the centre of the city over 32 storeys high. The population of Paris dropped from 2,850,000 in 1954 to 2,152,000 in 1990, as middle-class families moved to the suburbs. A suburban railway network, the RER (Réseau Express Régional), was built to complement the Métro; the Périphérique expressway encircling the city, was completed in 1973.