Experts believe the objet is handmade and have dated it as up to 250,000 years old.
But humans didn’t regularly produce aluminium products until about 200 years ago – baffling archaeologists.
Alien hunters has suggested the artefact wasn’t worked by human hand at all – as it is part of a UFO.
Builders working on the shores of the Mures River not far from the central Romanian town of Aiud found three objects 33ft underground.
They appeared to be unusual and very old, and archaeologists were bought in who immediately identified two of them as being fossils.
The third looked to be a piece of manmade metal – although very light – and it was assumed to be an axe head.
All three were sent for further analysis.