There was a much-derided alternative plan for the Paris train system, put up by the imaginative sea captain, Edouard Mazet in 1884. He proposed a system which used neither rails, nor wagons, nor bridges, nor tunnels.
He reasoned that it was impossible to fit an underground sytem under a town that was already built, and that it wouldn’t work building one before a town was constructed as there wasn’t anyone there to use it. Therefore the system would have bypassed the need to dig up a thriving and overcrowded city to build new tunnels.
Overground railways weren’t much better in Bazet’s eyes. They were seen as a blight on a city with the necessity of having bridges and viaducts to conduct them. Mazet therefore came up with a “boat” system whereby boat wagons would slide between a series of lampposts set closely together. The boat would be long enough so that each end could rest on a post.
Another advantage of this system was that the boats would not be boardable while they were on the go, thereby preventing thefts.
It was never explained how the boats would be propelled, and it’s unlikely that the technology existed at the time to make it successful – which is probably why the Metro was built instead!
(Incidentally, lines along the Grands Boulevards were based on Mazet’s plans as part of metro lines 8 and 9 – the boy wasn’t so mad after all.)