It turns out the shiny monolith that was spotted in a remote southeastern Utah desert two weeks ago was not the only such object to mysteriously appear.
The alien-looking object was discovered in the US on November 18 before disappearing in equally baffling fashion on Friday evening.
Now it transpires a similar looking object has been found in Romania.
The four-metre tall upturned triangular prism appeared on Thursday on a hillside outside Piatra Neamt in the north of Romania, close to an important archaeological site.
A dark metallic structure that appears covered in concentric circles, it was spotted a few metres away from the well-known archaeological landmark the Petrodava Dacian Fortress, an fort built by the ancient Dacian people between 82 BC and AD 106.
"There is no reason to panic for those who think there is still life in the universe," local mayor Andrei Carabelea wrote on Facebook.
"My guess is that some alien, cheeky and terrible teenagers left home with their parents' UFO and started planting metal monoliths around the world. First in Utah and then at Piatra Neamt. I am honoured that they chose our city."
He said it would have been better if they had obtained a building permit but he said they would be lenient if the object attracted tourists.
The object in Utah touched off international sci-fi speculation, recalling the classic Stanley Kubrick 1968 film, "2001: A Space Odyssey."
In the Kubrick movie, an alien monolith is a recurring symbol that appears to play a role in the development of human evolution.
The riddle in the desert, twice as tall as an average adult, drew scores of the curious to see it, even though its exact location was not made public, according to accounts on social media.
And just as no one knows where it came from, no one seems to know where it went.
Neither the federal Bureau of Land Management nor the state's Department of Public Safety said they had any idea.
"We have received reports that the illegally installed structure, referred to as the 'monolith' has been removed from Bureau of Land Management public lands by an unknown party," the state agency posted on Saturday on its website.