More than 10,000 people marched in the city of Messina in Sicily to protest the planned construction of a bridge linking the island to mainland Italy.
Thousands marched through Messina streets to voice their opposition to a bridge they say would damage the environment.
But Prime Minister Silvio Berlusconi and his center-right government have trumpeted the project as a vital driver of development in the south that will finally make Italy one nation by linking Sicily to the mainland.
Protesters argue the project would waste millions of euros.
A woman said she is protesting because Messina needs much more than a bridge. She added that the bridge would not solve the problems of development existing in southern Italy.
Speaking before the demonstration, the World Wide Fund for Nature said a new environmental study is needed, following a reclassification of the area's status by the European Union. Land affected by the bridge project on both sides was recently granted special EU protected status due to its unique bird and wildlife population.
There have also been fears of potential Mafia involvement in the project.
The Berlusconi government has dismissed those fears by stressing the economic benefits the bridge will bring.
The Messina bridge is without a doubt an ambitious project and one of the biggest ever undertaken in Europe. It has been on the drawing board since the 1960s and Prime Minister Berlusconi wants to be credited with actually making it happen.
If built, the nearly four-kilometer suspension bridge linking Sicily to the mainland will have the longest main span in the world. It will carry a double six-lane highway and four tracks for a high-speed railway line.
Work is expected to begin this year and be concluded by 2012.