A strange metallic artifact found in Romania in 1973 is puzzling scientists. Some even see it as a possible hint of alien visits to Earth in the past.

The chunk of metal was dug out of the bank of the river Mures in the town of Aiud, buried under 33 feet of sand. The builders who found it thought it might have been an axe head.

It was sent to Lausanne, Switzerland, for analysis, and that is when the mystery started. Analysis showed that it was composed of 12 different metals but was 90% aluminum. It was also dated to somewhere between 400 and 80,000 years old — but humans have only been able to produce metallic aluminum for 200 years.

The scientists were unable to determine the purpose of the metal piece, but some say its shape hints that it could be part of a complex mechanical system.

The metal is currently on display in the history museum of the Romanian city of Cluj-Napoca. Scientists are no closer to solving its puzzle than they were in 1973. Some still think it could be the work of alien visitors.

The president of the Romanian Ufologists Association, Gheorghe Cohal, has stated that there is no known human technology that could produce the particular combination of metals used in the piece.