Article: The Paris region hosts France's highest concentration of the grandes ecoles 55 specialised centres of higher-education outside the public university structure. The prestigious public universities are usually considered grands etablissements. Most of the grandes ecoles were relocated to the suburbs of Paris in the 1960s and 1970s, in new campuses much larger than the old campuses within the crowded city of Paris, though the Ecole Normale Superieure has remained on rue d'Ulm in the 5th arrondissement. There are a high number of engineering schools, led by the Paris Institute of Technology which comprises several colleges such as Ecole Polytechnique, Ecole des Mines, AgroParisTech, Telecom Paris, Arts et Metiers, and Ecole des Ponts et Chaussees. There are also many business schools, including HEC, INSEAD, ESSEC, and ESCP Europe. The administrative school such as ENA has been relocated to Strasbourg, the political science school Sciences-Po is still located in Paris' 7th arrondissement and the most prestigious university of economics and finance, Paris-Dauphine, is located in Paris' 16th. The Parisian school of journalism CELSA department of the Paris-Sorbonne University is located in Neuilly-sur-Seine. Paris is also home to several of France's most famous high-schools such as Lycee Louis-le-Grand, Lycee Henri-IV, Lycee Janson de Sailly and Lycee Condorcet. The National Institute of Sport and Physical Education, located in the 12th arrondissement, is both a physical education institute and high-level training centre for elite athletes.

Now answer this question: During which time frame were most grandes ecoles relocated?
1960s and 1970s