Milan’s Expo 2015 trade fair has now become the centre of a corruption inquiry.
Several other large public projects, including high-speed rail contracts and the building of a highway in Libya, have also come under investigation amid suspicions of fraud.
Four men have been detained by the police, including a former manager at the public works ministry, Ercole Incalaza, who is being held on suspicion of bribery.
The public works in question are believed to be worth some €25 million.
The investigation is also looking at 50 other individuals, including some politicians.
Investigators suspect that contracts were awarded after bribes had been paid to certain officials.
The Milan Expo, due to open on 1 May, was dogged by a series of alleged scandals last year. The development of the high-speed TAV rail network has also the focus of corruption allegations.
In February, the EU launched a fraud investigation into the rail line between Lyon and Turin which is being built.
In December, police arrested 37 suspects in and around Rome, in a similar crackdown on alleged corruption in the awarding of public works contracts.
