A group of amateur archaeologists performing surveys of derelict World War II bunkers in Italy have uncovered an ancient prehistoric monument dating back more than 5,000 years.

The incredible find occurred early in 2016 when the friends came across an unusual arrangement of rocks overlooking Gela, a town on Sicily's southern coast. Even more intriguing was the discovery of a 3.2-foot diameter hole in one of the larger rocks at the site.

"It appeared clear to me that we were dealing with a deliberate, man-made hole," archaeologist Giuseppe La Spina told Seeker. "However, we needed the necessary empirical evidence to prove the stone was used as a prehistoric calendar to measure the seasons."

After almost three months of studying the site, La Spina decided to test his calendar theory during the winter solstice on Dec. 21, 2016. Using a compass, cameras and an aerial drone, the team took to the skies and recorded the perfect alignment of the rising sun through the hole.

"At 7:32 a.m. the sun shone brightly through the hole with an incredible precision," La Spina said. "It was amazing."

You can see video of the dramatic moment below:

In addition to several undisturbed tombs dating back to the Bronze Age found near the site, La Spina and his team also discovered a fallen 16.4-foot menhir, or large upright rock, that apparently tied into the site's sundial.

"It stood at a distance of 26 feet, right in front of the rock's hole," La Spina added.

Based on early investigations, the archeologists estimate the site dates back to between 6000 and 3000 B.C.

"Making an archaeological discovery is in itself an important event, but to be part of one of the most sensational finds in recent years fills me with pride," La Spina told The Local.

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Amateur archaeologists stumble upon ancient Italian 'Stonehenge'
The sundial found in an arrangement of rocks overlooking the town of Gela on Sicily's southern coast dates back to between 6000 and 3000 B.C.