Archaeological treasures tease us with their window into ancient history, customs, and people. Sometimes they even suggest that we’ve been visited by beings from other worlds…

1. Stonehenge

Stonehenge Andi Hess/Shutterstock

Located on a flat plain north of Salisbury, England, Stonehenge is a circular formation of massive stones (the largest are 30 feet tall and weigh 25 tons). Scientists believe it was a monument marking a massive burial site that was built between four and five thousand years ago. No one has ever been able to figure out how or why the monument was built—or whether it was even built by humans; archaeologists this past month uncovered evidence that at least two of the stones had been in place long before humans dwelled on Earth, shares Forbes.

2. Super-henge

Super-henge Vienna Institute For Archaeology/Shutterstock

In 2016, just two miles from Stonehenge, scientists discovered what they thought was another mysterious stone monument and gave it the name, “Super-henge.” But a year later, archaeologists discovered that it wasn’t stones at all, but rather hundreds of timber posts in massive pits that had once been arranged in a circular fashion sometime before 2450 B.C. Even more mysterious is that evidence has been discovered that the posts had been removed only a short time after having been placed. 

3. America’s Stonehenge

America’s Stonehenge Jim Cole/Shutterstock

Originally known as “Mystery Hill,” this archaeological site in Salem, New Hampshire consists of both rocks and stone-structures. Although it takes its name from the English archeological site, it’s much smaller and much, much younger overall. It was first reported as being discovered in 1937 by William Goodwin, who purchased the land on which it sits. Some have accused Goodwin of creating the site, but archaeologists have carbon-dated at least some of its contents to 2,000 B.C. But that’s pretty much all that’s known about it.

4. The Serpent Mound

The Serpent Mound Seen Unseen Media/Shutterstock

The 1,300-foot high and three-foot-high mound located on an Ohio plateau is the largest model of a serpent in the world. Some researchers believe it was constructed by a local native tribe around 300 B.C., but are still unsure of the exact culture that may have erected this massive effigy.  More recently, Brad Lepper, Ph.D, proposed in a paper published earlier this year in the Cambridge Archaeological Journal that the imagery is consistent with that of Native Americans from about 1,000 years ago. . 

5. The stone spheres of Costa Rica

The stone spheres of Costa Rica Inspired By Maps/Shutterstock

In Costa Rica’s Diquis Delta region, 300 stone balls were discovered in the late 19th century, the largest being eight feet in diameter and weighing 16 tons. Although it appears the balls were made by hammering rocks, so far, no one figured out who made them or why. Some even believe they were placed by extraterrestrials, and still, others believe they could be relics from the “lost” city of Atlantis.

6. The lost city of Atlantis

The lost city of Atlantis Kharbine-Tapabor/Shutterstock

Speaking of Atlantis, did you know there’s no one place on earth that’s known to be the site of the island described by Greek historian Plato in 360 B.C. as having sunk into the sea over 10,000 years ago? People have claimed to have discovered it all over the world, in places like the Bahamas or Cuba, and most recently in the waters around Micronesia. Without actual archeological relics to study, and since it’s based entirely on ancient writings, the mystery of Atlantis may be an archaeological case of the tail wagging the dog, but it could be out there, and so continues to captivate our imagination. 

7. King Tut’s tomb

King Tut’s tomb Str/Epa/REX/Shutterstock

King Tutankhamun was just nine years old when he ascended to the throne of Egypt in the 1300s B.C., and he was scarcely an adult when he died at 17, but he stands at the center of several archaeological mysteries—first and foremost: the circumstances surrounding his death. Because his mummified body appears to have caught fire after his tomb was sealed, archaeologists believe he was buried very quickly, leading to a botched embalming job that allowed a fire to erupt as a chemical reaction between oxygen and embalming oils.

8. The Great Pyramids of Egypt

The Great Pyramids of Egypt

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