On 8 December 1977, President Valery Giscard D'Estaing formally inaugurated the most ambitious transport system in the French capital since the launch of the first metro nearly 100 years before.
Crossrail is likely to be similar to France's RER
The Paris equivalent of London's mooted Crossrail link was called the RER - the Regional Express Network - and more than a quarter of a century on it has become an integral and highly successful part of the city's infrastructure.
The idea went back to the early post-war years.
Paris planners realised the city was endowed with two functioning but unconnected rail systems - the metro, run by the RATP (Regie Autonome des Transports Parisiens), and the suburban trains, run by the SNCF (Societe Nationale de Chemins de Fer).
"The authorities worked from the premise that the metro is like a prisoner within its own straitjacket... while the suburban lines ended in a cul-de-sac at the main Paris stations, which prevents an efficient diffusion of passengers," states the RER's official history.
The 1960s and early 70s were a time of enormous confidence and growth in France, and also of rigidly-controlled central planning. Every five years the magnificently-named General Commission for the Plan (which still exists) would set out on-coming projects and budget money accordingly.
That was how the enormous task was undertaken of blasting through new tunnels under central Paris to take the wide-gauge regional trains, and then constructing a series of mammoth stations to link the lines to the metro.
The first lines - RER A and RER B - ran west-east and north-south, meeting at the enormous Chatelet station under the old Les Halles market, which was being re-developed at the time.
Charles-de-Gaulle and Orly airports were linked together, and the gleam-in-the-eye that was to be the La Defense office complex to the west became part of the city proper.
Photographs of the era give an indication of the scale of the undertaking, as engineers dug beneath historic areas of the capital, and the Etoile, Auber, Nation and St-Michel stations all emerged from vast building sites.
The system has spread further, and there are a total of five RER lines with numerous different branches. By a quintessentially French quirk, the three new lines are run by the SNCF, which also controls the top end of RER B. This means that at the Gare du Nord an SNCF driver has to take over from a metro employee.
More than a million passengers a day travel on the A and B lines, and a slightly smaller number on the other three. The system is zoned for pricing purposes into eight concentric circles, with zone 1 central Paris and zone 8 some 30 miles away.
The cost of the entire enterprise is impossible to calculate, but it runs into billions of euros spread over 30 years. A government note from the early days shows that the high cost was not uncontroversial.
According to the history, it spoke of "the proliferation of installations and the under-estimation of prices, the omnipresent 'luxury' serving no apparent purpose. In short it looked like the money of French taxpayers was being poured away for the sole prestige of Parisians."
If the system remains extremely busy, the main complaints from suburbanites concern security and strikes. For foreigners the main problem is the difficulty of discovering what train goes where. Each has a letter-code, which is gobbledigook to the uninitiated.
The other challenge of course is how to pronounce the thing. Many a train has been missed because of the inability of all non-French to say the letters R. E. R. in a manner intelligible to the natives. It is a true shibboleth.
As a rough guide, just say : "Air!- errr - Air!"