Proponents of this theory argue that ancient artwork may hide signs that aliens have visited humanity.
Paintings drawn centuries ago, cave paintings and tapestries contain symbols and shapes that resemble UFOs and aliens.
But art historians say this is simply a misconception of religious symbols or figures.
Let's take a look at these works of art and consider whether they really depict UFOs and aliens or something else.
Annunciation with Saint Emidius, 1486
The painting by the Italian artist Carlo Crivelli was painted in 1486. It captures the moment when the Archangel Gabriel conveys the message to the Virgin Mary that she will give birth to Jesus.
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Proponents of the theory suggest that the disc shown in the upper left corner and shedding light on Mary is a spaceship.
But experts say it's just a group of angels forming a circle in the sky. The ring and the light streaming from it symbolize the holy spirit emanating from the Virgin Mary.
Illustration from the book "Ume No Chiri", 1844
Urobune is a mysterious, unknown object that was found drifting off the coast of East Japan in 1803.
The object is depicted in three different Japanese texts, including the book Ume No Chiri, 1844.
The picture shows a UFO-like object that Japanese sailors found floating in the ocean.
The description states that the object was made of steel and glass and was large enough to accommodate an average person.
Inside, the sailors found strange inscriptions that they could not decipher.
Glorification of the Eucharist, 1600
This 17th century painting by Italian artist Bonaventure Salimbeni depicts God the Father and Jesus. They look down to God's Kingdom.
But the strange, circular object between them resembles the Russian space satellite launched more than 350 years later in 1957.
Proponents of the theory argue that: "Such similarities cannot be mere coincidence."
Saint Wolfgang and the Devil, 1475
The famous 15th century artist Michael Pacher was inspired to create this painting by the legend of St. Wolfgang, who convinced the devil to help him build the church.
St. Wolfgang was Bishop of Regensburg in Bavaria in the 10th century.
Proponents of the theory argue that the figure of the devil in the painting may be an image of an alien who visited Earth.
But this is highly questionable, given that the devil has been represented in a wide variety of strange forms throughout the long history of religious art.
Baptism of Christ, 1710
Art critics believe that this picture illustrates a passage from the Holy Scriptures: "The heavens were opened to Him, and John saw the Spirit of God, who descended like a dove and descended on Him."
It was painted by the Dutch artist Art de Gelder in the 18th century.
Proponents of the theory speculate that the disc-shaped object shining bright light on John the Baptist and Jesus may be a UFO.
“The artist wanted to convey the message that Jesus was related to aliens and may have been of extraterrestrial origin.
6th century Peruvian cave painting
The ancient Peruvians who inhabited the Nazca plateau are known for leaving behind huge cave paintings.
Many of these were made between the first and sixth centuries.
This drawing depicts a figure that is believed to look like an alien.
It is believed that the locals carved this figure to inform the aliens that they value their visits.
But this image is just as likely to be a message to the ancient Peruvian gods.
Madonna and Saint Giovannino, 15th century
In this painting, the Italian Renaissance artist Domenico Ghirlandaio depicts Mary, the mother of Jesus, looking at her two children.
The painting can be seen in Florence at the Palazzo Vecchio.
In the upper right corner above Maria, you can clearly see a disk-shaped object. A shepherd can be seen on the shore in the distance, peering into this object in the sky. He covers his eyes with his hand, possibly because the object is metallic and glistens in the sun. According to proponents of the theory, the object looks strikingly similar to the UFO as it is presented today.
But opponents of the theory say that artwork from that era often depicted clouds pouring out divine light as religious symbols.
Svetlana Bodrik