Soon after, they alerted police to the discovery and explained that them keeping it for themselves was not an option.

“There are so many coins and bars – it would be almost impossible,” the site manager Mario told VRT.

“Besides, that would be theft.”

Kobe agreed: “€9m – you simply can’t keep that hidden.”

The property currently belongs to CAW Oost-Vlaanderen, which provides welfare support in Dendermonde, a Flemish community of around 47,000 people.

Its director, Geert Hillaert, said his first reaction was “surprise and amazement”, adding that he hoped the loot might eventually be used to support the charity’s work and meet the “enormous need we experience daily”.

Local police urged the public not visit the active construction site looking for treasure.

The force – which has updated its Facebook profile picture to an image of a gold coin – said it hoped the discovery would end up in “the right place” and change people’s lives.

The rightful owner has five years to claim the hoard under Belgian law – though the local prosecutor, who has launched an investigation, said it was not yet known who this might be.

If no one comes forward, civil law states that hidden treasure on someone else’s property be divided between the finder and the property’s owner.

This only applies, though, if the loot is not found to be linked to criminal activity.

Both the builders and the charity now face a wait of up to 1,823 days for an owner to come forward. If no one speaks up to successfully claim it, silence truly will be golden.