France and Italy have signed an agreement to build an €8.5bn (£7.1bn) high speed rail link between Lyon and Turin.
French and Italian Ministers met to give the go ahead to the line, which will slash travel time from seven hours to just four and is due to be completed by 2023.
However, protests have been taking place in Italy where local people say traffic levels are falling so the line is not necessary and building it will damage the environment.
Demonstrations have involved clashes with the police.
Work is reported to have already started last summer in the Susa Valley, Italy, with police on hand in case of trouble.