ROME (AP) -- Thousands of people marched in the Sicilian city of Messina on Saturday to protest a government plan to build a bridge that would connect the Italian mainland with Sicily in a massive 13.5-billion-euro ($15.5 billion) infrastructure project.

Protesters staunchly oppose the Strait of Messina Bridge project over its scale, earthquake threats, environmental impact and the specter of mafia interference.

The idea to build a bridge to connect Sicily to the rest of Italy has been debated off and on for decades but always delayed due to these concerns. The project, however, took a major step forward when a government committee overseeing strategic public investments approved the plan this week.

Transport Minister Matteo Salvini, the project's main political backer, called it "the biggest infrastructure project in the West."

Salvini cited studies estimating the project would create up to 120,000 jobs annually and help stimulate economic growth in economically lagging southern Italy, as billions more are invested in surrounding road and infrastructure improvements.

Opponents are not convinced by these arguments. They are also angry that about 500 families would have to be expropriated in order for the bridge to be built.

"The Strait of Messina can't be touched," protesters shouted as they marched in Messina. Many carried banners that said "No Ponte" (No Bridge). Organizers estimated crowd size at 10,000 people.

The proposed bridge would span nearly 3.7 kilometers (2.2 miles) with a suspended section of 3.3 kilometers (more than 2 miles). It would surpass Turkey's Canakkale Bridge by 1,277 meters (4,189 feet) to become the longest suspension bridge in the world.

Preliminary work could begin as early as late September or early October, pending approval from Italy's Court of Audit. Full construction is scheduled to begin in 2026, with completion targeted between 2032 and 2033.

Plans for a bridge have been approved and canceled multiple times since the Italian government first solicited proposals for one in 1969. Premier Giorgia Meloni's administration revived the project in 2023.

With three car lanes in each direction flanked by a double-track railway, the bridge would have the capacity to carry 6,000 cars an hour and 200 trains a day -- reducing the time to cross the strait by ferry from up to 100 minutes to 10 minutes by car. Trains would save 2/12 hours in transit time, Salvini said.

The project could also support Italy's commitment to raise defense spending to 5% of GDP targeted by NATO, as the government has indicated it would classify the bridge as defense-related.

Italy argues that the bridge would form a strategic corridor for rapid troop movements and equipment deployment, qualifying it as "security-enhancing infrastructure."

Environmental groups, however, have lodged complaints with the EU, citing concerns that the project would impact migratory birds.

Italy's president has also insisted that the project remain subject to anti-mafia legislation that applies to all large-scale infrastructure projects. Salvini pledged that keeping organized crime out of the project was a top priority.