Protesters demonstrating against a planned high-speed rail link with France clashed with police on Thursday amid concern that anger over the project could mar the 2006 Winter Olympics in the northern area.
At least two policemen and one protester were reported injured in the clashes, in which police in anti-riot gear fired teargas to control one group of demonstrators.
Tens of thousands of protesters, arguing the link will harm the environment, had massed along Alpine roads in the Susa valley near Turin, the city that will be the main host for the February Games.
The valley is nestled near the Italian-French border, and connects the main venues for the Olympics.
The demonstration started peacefully but police then cordoned off the main road leading to the village of Venaus. Scuffles broke out when some protesters tried to push through. Police used truncheons and tear gas to fight back around 100 activists who had entered a construction site near Venaus.
"They're hitting people. I'm a primary school teacher and I have always told children that Italy is a democracy - I can't say that any more," said Venaus resident Alan Bruno.