Train from Paris to Rome

I have been researching since we will do this in March. Check the SNCF site for schedules and prices. Takes about 11.5 hours on the fast trains.

Super slow.
With the French TGV (high speed train) you can travel to Milan in just over 7 hours. The train arrives at the Milan Garibaldi station. Unfortunately the rail line through the Alps between Chambery and Turin does not allow high speeds.
Then from Milan Garibaldi you need to switch to a Frecciarossa to Rome (another 3.5 hours).
11 hours is the best you can hope for.
The Thello night train is a 15 hour journey.
Paris to Rome is generally best by air, unless you absolutely want to do it by train, for whatever reason.

Also: the French TGV arrives at Milano Porta Garibaldi station. From there, you either go on with an Italo train, that arrives at Roma Tiburtina or Roma Ostiense but not at Roma Termini, or you transfer by taxi or metro to Milano Centrale where Frecciarossa trains travel to Roma Termini. The conveniente/inconvenience of all this depends on your final destination in Roma.

Railway travel is convenient on short and middle (up to 600 kms) distances. As distances grow, railways cannot compete on price and convenience with airplanes - so the railway companies do not even bother to offer viable alternatives.

But if you are a train fancier like my DH, 11 hours is a good start. We are looking forward to doing this because it's not outrageously expensive if you buy in advance, we are not in a rush, the trains are nice (and most of all are NOT planes), it's relaxing, we can read, play on the internet, talk to each other, walk around. We have solved many societal problems while ahving significant conversations on the train. :-) On the plaen almost none of that is possible and your ears hurt too.

I will do almost anything to avoid flying. Such a cattle call!

I have done that trip by train before and rather like it. I'm contemplating it for a trip in March.

I prefer a slightly different (and for me very cheap) route - Paris (Est) to Strasbourg, Basel to Milano, Milano to Roma with an overnight in Basel or Milano.

I actually start my trip north of London so also benefit from the Eurostar.

I could fly faster and cheaper but don't always want to.