It's expected to cost €26 billion to complete with the construction of a trans-alpine tunnel swallowing up over €18 billion.
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Thousands of Italians have protested against their government agreeing to resume work on the controversial high-speed Turin to Lyon railway link.
It's an ambitious engineering feat that involves finishing a 57.5 kilometre-long tunnel under the Alps to connect France and Italy.
Italian prime minister Giuseppe Conte said this week that blocking work on the link would cost Italy more than completing it.
The long-running saga, which has faced opposition from environmentalists and local communities, is splitting Italy's current coalition.
Matteo Salvini's League party support the project but its governing party, the Five-Star Movement, opposes it.
On Saturday, Italian protesters marched to one of the construction sites.
Agreement on resuming the project came after Brussels made an offer: it will increase its share of the tunnel's funding from 40% to 55%.
If and when it's completed the journey time between Milan and Paris will go down from nearly seven hours to just four hours.