Introduction

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Puzzling ancient finds have a way of captivating the public, perhaps because it's just too easy to dream up interesting explanations for how and why things exist.

These 25 archaeological discoveries have left people in awe — and left scientists scratching their heads — year after year.

Stone spheres in Costa Rica

(Image credit: © Museo Nacional de Costa Rica / Juan Julio Rojas)

Giant stone spheres — some dating as far back as A.D. 600 — pepper the Diquis Delta of southern Costa Rica. Known locally as Las Bolas ("The Balls"), these monuments were the works of a Pre-Colombian civilization, and most are made from gabbro, a rock that forms from molten magma. The people who carved the stones into their perfectly spherical shapes likely did so using other small stones, according to archaeologists who study the ancient rocks.

Many non-experts have speculated that the so-called Diquis Spheres were used for astronomical purposes, while others think they may have pointed the way to significant places. The truth is that no one knows for sure. The Chibchan people who once populated Costa Rica and other parts of Central America vanished in the wake of the Spanish conquest, and the purpose of the spheres vanished with them, John W. Hoopes, an anthropologist at the University of Kansas, told JSTOR Daily in January 2016.

Antikythera mechanism

(Image credit: Antikythera Mechanism Research Project)

Like something from a fantastical treasure movie, the discovery of the Antikythera Mechanism remains a major archaeological head-scratcher.

Found in the sunken wreckage of a Greek cargo ship that is at least 2,000 years old, the circular bronze artifact contains a maze of interlocking gears and mysterious characters etched all over its exposed faces. Originally thought to be a kind of navigational astrolabe, archaeologists continue to uncover its uses and now know that it was, at the very least, a highly intricate astronomical calendar.

It is still the most sophisticated device ever found from that period, preceding the next appearance of similar devices by 1,000 years.

Cleopatra's tomb

(Image credit: Artist: Lawrence Alma-Tadema)

Cleopatra VII was the last of a series of rulers called the Ptolemies who ruled Egypt between 305 and 30 B.C. Much is known about her intelligence, beauty and romantic relationships (she had children with both Julius Caesar and Mark Antony), but one fact about Cleopatra is still shrouded in mystery — her burial place.

Cleopatra and Antony both committed suicide after their former ally, Octavian, defeated them at the Battle of Actium in 31 B.C. The two were buried together at a site that the writer Plutarch (A.D. 45-120) described as a "lofty and beautiful" monument, located near a temple of the Egyptian goddess Isis. But exactly where this tomb is located remains a mystery. If anyone ever finds the lovers' tomb, there's a chance it might be empty, as grave robbery was not uncommon in ancient times, according to archaeologists.

Qin Shi Huang's tomb

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In 1974, farmers in China's Shaanxi province accidentally unearthed one of the biggest archaeological finds of the 20th century — the life-size terracotta armyof Emperor Qin Shi Huang (259 B.C. – 210 B.C.).

The intricately carved figures aren't a mystery: Historians know that the clay army was created to defend China's first emperor in the afterlife. What isn't known, however, is where exactly the emperor is buried or what treasures his burial chamber might contain. [See Photos of the Ancient Terracotta Warriors]

A pyramid-shaped mausoleum is located about a mile to the northeast of where the terracotta army was discovered. However, no one has actually entered the mausoleum that holds Qin Shi Huang's remains.

The first emperor's final resting place is the most opulent tomb ever constructed in China, according to ancient documents describing its construction. An underground palace, complete with a surrounding "kingdom," the mausoleum is made up of a network of caves and even included a state-of the-art drainage system. Whether archaeologists will ever have the technology they need to safely excavate the tomb (which also happens to contain extremely high levels of mercury) remains a mystery, as do the many treasures that lay inside.

Atlantis

(Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team)

The lost city of Atlantis has been discovered in the Bahamas, the Greek Islands, Cuba, and even Japan if every claim was to be believed.

First described by the ancient Greek historian Plato in 360 B.C., the mythological island was supposedly a great naval power before sinking into the sea over 10,000 years ago in a catastrophic event.

Archaeologists debate the actual historical existence of the island as well as its most plausible location if it ever actually existed among the many sunken ruins discovered around the world. But even without definitive proof, Atlantis continues to engage the popular imagination like few other archaeological mysteries out there.

Stonehenge

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Sprucing up an otherwise docile English field, the prehistoric monument commonly known as Stonehenge is one of the world's most famous landmarks.

The ring of megalithic stones was built approximately 4,000 years ago and was an impressive feat for the primitive people who constructed it but that's about all archaeologists know for sure. None of the theories on the original purpose of Stonehenge, which range from an astronomical observatory to a religious temple of healing, has ever been, well, set in stone.

Ancient animal traps

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Low stone walls crisscrossing the deserts of Israel, Egypt and Jordan have puzzled archaeologists since their discovery by pilots in the early 20th century.

The chain of lines some up to 40 miles (64 kilometers) long and nicknamed "kites" by scientists for their appearance from the air date to 300 B.C., but were abandoned long ago.

The mystery might be somewhat clearer thanks to a recent study claiming that the purpose of the kites was to funnel wild animals toward a small pit, where they could easily be killed in large numbers. This efficient system suggests that local hunters knew more about the behavior of local fauna than previously thought.

Nazca lines

(Image credit: NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team)

From the ground, the Nazca Lines of Peru are nothing spectacular. However, seen from the air, from which they were first spotted by commercial aircraft in the 1920s and 30s, they are staggering.

Archaeologists agree the enormous shapes there are hundreds of them, ranging from geometric lines to complicated depictions of animals, plants and imaginary figures were made over 2,000 years ago by people of the pre-Inca Nazca culture, who simply removed the red surface pebbles to reveal the lighter earth below in designs of their choice.

Just why they did it remains enigmatic, prompting conspiracy theorists to float ideas about alien landings and ancient astrology. The lines were more likely to have been a ritual communication method with the Nazca's deities, say archaeologists.

The Great Pyramids

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Even the information that archaeologists do know about the Great Pyramids of Egypt is enormously fascinating, to say nothing about what still might be uncovered.

Built almost 5,000 years ago in what is now Cairo, the three-pyramid complex with the largest, Khufu, dominating the site is a testament to the ancient Egyptians' reverence for their Pharaohs and the intricacies of their belief in the afterlife.

Archaeologists are still discovering new tunnels and shafts built within the pyramids, and are still searching for clues on who built the great monuments, how and why, even today.

Shroud of Turin

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Perhaps no archaeological discovery is more debated than the enigmatic Shroud of Turin, which many believe to be the burial shroud of Jesus Christ. This long piece of twill cloth bears traces of blood, as well as the darkened imprint of a man's body.

The Catholic Church officially recorded the existence of the shroud in A.D. 1353, which is when the cloth showed up in a church in Lirey, France. But the legend of the shroud dates back to A.D. 30 or 33. According to that legend, the shroud was transported from Judea (now southern Palestine) to Edessa, Turkey, and later to Constantinople (now called Istanbul). When crusaders sacked Constantinople in A.D. 1204, the cloth was moved to Athens, Greece, where it was allegedly held until A.D. 1225.

It wasn't until the 1980s that researchers got their hands on the cloth to try to determine its true age using radiocarbon dating. They determined that the alleged burial cloth of Jesus was actually created between A.D. 1260 and A.D. 1390. In other words, the scientists determined that the cloth is most likely a medieval forgery. However, critics of this research argue that the scientists may have dated newer portions of the shroud that were stitched together centuries after Jesus' death, which would explain why the shroud seems "newer" than it really is.