It all depends on the water level.

If there's been plenty of rain, there's nothing out of the ordinary to be seen in the Valdecañas Reservoir in the province of Cáceres, Spain. But as conditions start to dry up, the peaks of granite stones begin to emerge. These make up the remains of a megalithic monument called the Dolmen of Guadalperal, also known as the Spanish Stonehenge.

This summer, the water level has dropped so low that the monuments have dramatically reemerged.

"All my life, people had told me about the dolmen," Angel Castaño, resident of a nearby village and president of the local Raíces de Peralêda cultural association, tells Atlas Obscura. "I had seen parts of it peeking out from the water before, but this is the first time I've seen it in full. It's spectacular because you can appreciate the entire complex for the first time in decades."

The dolmen are usually submerged in the water. The dolmen are usually submerged in the water. (Photo: 1080 Wildlife)

The monument is believed to be anywhere from 4,000 to 7,000 years old. Often referred to as the "treasure of Guadalperal," the collection of 140 vertical stones were most likely erected as a solar temple and a cemetery.

Until time and water erosion took their toll, the monument also included menhirs — tall, standing stones — topped with horizontal stones that made a single-chambered tomb called a dolmen, reports El Espanol. A menhir engraved with sculpted symbols and a snake guarded the entrance. Later on, a pebble wall was built around the dolmen to create a collective burial site.

Submerging the past

Some of the stones have fallen or cracked over the years. Some of the stones have fallen or cracked over the years. (Photo: Rubén Ortega Martín/Raíces de Peralêda)

Although people have been aware of the monument for centuries, it wasn't until the mid 1920s that German researcher Hugo Obermaier first excavated the site. His research wasn't published until 1960. By the time others began to realize the magnitude of this massive structure, it was under water.

A government engineering project prompted construction of the Valdecañas reservoir in 1963, when the dolmen were covered with water. And it wasn't the only archaeological site submerged in the name of modernization.

"You couldn't believe how many authentic archaeological and historic gems are submerged under Spain's man-made lakes," Primitiva Bueno Ramirez, a specialist in prehistory at the University of Alcalá, tells Atlas Obscura.

This menhir has a map of the river Tagus, and other carvings that might be other rivers as well as a map of the sky. This menhir has a map of the river Tagus, and other carvings that might be other rivers as well as a map of the sky. (Photo: Alejandro Rufo/Raíces de Peralêda)

Over the years as the water levels fluctuated, parts of the stones would occasionally emerge. But this is the first time the whole monument has been visible.

After 56 years underwater, the elements have taken their toll. Some of the granite stones have fallen and others are cracked, according to Smithsonian. There's an online petition to save the dolmen, and some cultural preservationists are urging for it to be moved to dry land.

"We move to save the heritage, and now is the time," says a statement from the cultural association Roots of Peraleda to El Espanol. "We want to value this monument to promote tourism, so it would have to be repositioned without separating it from its context."

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

Drought reveals 'Spanish Stonehenge'
The remains of a megalithic monument, the Dolmen of Guadalperal, have resurfaced in Spain.