A 500-kilogramme bomb caused quite the scare on Thursday in Mantes-la-Jolie, a town in the Yvelines department to the west of Paris.
The explosive - understood to have been from the Second World War - was found on a construction site at around 3.30pm, the local prefecture said in a statement.
BFM TV reported that it was a bomb dropped by Britain's RAF, although this is yet to be confirmed.
Before long, some 3,000 people living near the site were evacuated from their homes and nearby train traffic was interrupted.
Around ten streets within a 340-metre perimeter of the bomb site were closed to traffic and bomb technicians were called in for what authorities called a "delicate operation".
The two teams of experts managed to defuse the bomb by 10pm, reporting that it had contained 200 kilos of explosives.
By 11pm, the thousands of residents who had been waiting in nearby gymnasiums were allowed to return to their homes.
Despite the Second World War ending over 70 years ago, remnants continue to show up across France surprisingly regularly.
In February last year, trains from the Gare de L'Est station were delayed after a 250kg shell was discovered in a building site nearby.
In September 2014 a camper was killed when a suspected World War Two bomb exploded on Ile de Groix, an island off the north-west coast of France.