FROM Bible verses to ancient Egyptian hieroglyphs, history is full of strange goings on that alien hunters claim are proof of visits from extraterrestrials.
The earliest records could even be in the form of paintings by our caveman ancestors – perhaps showing that the UFO sightings now subject to official probes in Washington and Beijing are really nothing new.
Earlier this year, a long-awaited Pentagon report admitted experts could not explain some 144 reports of "unidentified aerial phenomena".
It was slammed as a "whitewash" by believers even though top brass said they could not rule out an alien origin for the sightings.
Meanwhile the Chinese government has reportedly launched its own UFO investigation after a rush of excitement there.
Military researchers are said to have dubbed them "Unidentified Air Conditions" or UACs.
China and Russia reportedly hope to take the international lead in studying encounters, sparking a bizarre new arms race with the US.
But as these examples show, people have been looking up in wonder for thousands of years.
11 'Heavenly' figures depicted in rock art from Siberia 5,000 years ago
Cave paintings and carvings dating back to 8,000BC have sparked great interest among alien watchers.
Stone age tribes created thousands of artworks called petroglyphs at Val Camonica in northern Italy.
The most famous depict long-limbed "astronauts" who appear to be wearing globe-shaped helmets with shining lights around them.
Some have claimed them as proof that visitors from outer space made contact and were worshipped as gods.
Meanwhile other cave paintings in Siberia from 5,000 years ago are said to show "heavenly" figures with horns and feathers on their heads.
Experts say the dyes used were made with a sophisticated scientific understanding far beyond what we might expect of Neolithic man.
Carvings from pharoahs' tombs show shining globes in the sky over awed crowds.
Archaeologists say this is because the ancient Egyptians worshipped the sun.
This has not stopped alien watchers from seeing it as evidence of flying saucers.
And there have long been theories that great monuments such as the Pyramids of Giza were built by aliens.
They claim the pyramids form a map of the stars, and it would have been impossible for humans to have built them so precisely.
Last year the Egyptian government officially denied any extraterrestrial link after Elon Musk tweeted support for the theories.
China's 'alien' civilisation
Bizarre bug-eyed statues found in south-west China have fuelled theories that aliens invaded the country in the Bronze Age.
More than 500 relics made of jade have been unearthed at the site of the former capital of the Xia Dynasty which ruled from 2070BC-1600BC.
The green colour and pointy ears are said to be evidence of contact with another civilisation.
The growing popularity of the theory even led to an official denial of any alien link.
"Some artistically exaggerated goddess statues cannot be said to be 'aliens,'" said Lei Yu, an archaeologist at the Sichuan Provincial Cultural Relics and Archaeology Research Institute.
The Bible's Book of Ezekiel describes how the prophet saw a flying chariot emerging from a whirlwind and a cloud of fire.
The chariot was carried by four human-like angels each with four faces, and below it were four mysterious wheels.
Scholars claim it was around 593BC in modern day Kuwait. But there has been fierce debate on how to interpret the verses.
Famed Swiss Ufologist Erich von Däniken claimed it was evidence of an alien visitation, rather than a vision from God.
He was so convincing that Nasa scientist Josef Blumrich later wrote a book explaining how such a craft would have operated.
Roman chronicler Livy left a fascinating account of "many prodigies" spotted in 214 BC, including "phantom ships" that were "seen gleaming in the sky".
The historian Plutarch wrote about an even more remarkable event during a battle in 74BC.
He said "with no apparent change of weather, the sky burst asunder and a huge, flame-like body was seen to fall between the two armies.
"In shape it was most like a wine-jar, and in colour like molten silver."
Thousands of onlookers, including enemy leader King King Mithridates VI, apparently confirmed the truth of the story.
Another eminent scholar, Titus Flavius Josephus, wrote about a "miraculous phenomenon defying belief" in the first century AD.
It involved "chariots and armed battalions hurtling through the clouds and encompassing the cities".
Princess from the Moon
One of Japan's most famous legends dating from around 1,000 years ago tells the story of “The Shining Princess”.
Kaguya is said to have been found as a baby inside a shining bamboo stalk, and when she grows up the Emperor is desperate to marry her.
But she rejects him explaining she is not from the Earth, and a craft arrives to take her home to the Moon.
Official records tell how a woman did arrive in Japan in a round vessel which some claim is a classic flying saucer shape.
The Nuremberg 'UFO battle'
In 1561, witnesses said they saw the sky filled with bright shining objects in Nuremberg, Germany.
They ranged from "blood-red semi-circular arcs" to dark balls of "black ferrous colour".
They rushed back and forth and "fighting among themselves", according to contemporary newsletters.
Eventually they fell onto the earth and "wasted away" with "immense smoke".
A similar UFO battle was reported five years later in Basel, Switzerland.
Witness said numerous red and black balls were "fighting" in the sky over several days, accompanied by unusual sunsets and sunrises.
Famous artworks are littered with aliens and UFOs, theorists claim.
One of the most convincing theories surround a painting called The Baptism Of Christ by Flemmish artist Aert De Gelder.
It shows a saucer in the sky shining down beams of light.
Leonardo's John The Baptist and the Mona Lisa are both said to show alien faces when a filter is applied.
A monastery mural in Kosovo from 1350 showing the Crucifixion is said to show two alien spaceships present.
And a Nativity scene has left Ufologists convinced it shows alien visitors.
The Madonna And Child With The Infant St John, by an unknown Florence artist has a shining eye-shaped saucer over Mary's shoulder.
Scholars are split over whether it is meant to be an angel.
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