In short: 

- Italy approved a 3.6km suspension bridge - the longest of its kind in the world 

- The project will cost $15.6 billion, but could help Italy meet defense spending targets

- Projected to create 120,000 new jobs annually during construction 

Thousands of protestors took to the streets in Messina over the Italian government's plan to build a suspension bridge connecting two key southern regions in Italy. 

Demonstrators held signs and banners with the slogan “No Ponte” (No Bridge). 

The protesters' concerns range from debate over its scale, earthquake threats, environmental impact and the specter of mafia interference.

Arguing it would have a massive environmental impact and would only damage the local population, claiming at least 500 families expected to be forced to leave their houses in the area where the construction works will start.

Angelica Donati, President of Italy's National Association of Building Contractors, says the monumental project will generate almost two times its cost - around 23 billion euros.

The Italian government says it will also create 120,000 annually over the course of construction in one of the poorest areas in Europe. 

Donati says there is some opposition to the bridge from green groups and economic groups in southern Italy worried their local businesses will be left financially ruined, but there are also many in favor of the project. 

"It's a massive injection of capital and of investment into an area that historically has seen very little investment, a region that struggles with very poor connectivity", she told CGTN Europe. 

The Italian government is hoping to classify what will be one of the world’s most ambitious engineering undertakings as military expenditure. It would allow Italy to meet its NATO military spending targets of five percent.  

Rome approved a suspension bridge stretching 3.6 kilometers across the sea – once complete, it’ll be the biggest single-arched bridge in the world. The $15.6 billion project will form a link across Mediterranean waters between the Calabria region and the island of Sicily. 

At the 2025 NATO summit, allies made a commitment to invest five percent of each country’s GDP (Gross Domestic Product) annually by 2035 to ensure defense readiness. Countries need to show they're making incremental progress to meet the target.

Beyond its big price tag, the engineering of the bridge will also be under intense scrutiny given its 400m height and plans for a two railway line down the centre with three lanes of traffic on either side. 

The sites' seismic activity over years is also being considered.

Back in 1908, a major earthquake hit the region, devastating Messina and other areas. However, Donati says a suspension bridge is one of the safest options given the location.  

"Suspension bridges are technically the best structural solutions for bridges in seismic zones", she says. "And the designers say that they very much accounted for the seismic risk and have chosen this structure."

Construction is expected to be complete by around 2032 or 2033.