Europe's persistent dry spell has caused water levels to plummet and submerged monuments to come to light, and one of them is the Dolmen of Guadalperal. Since 1963, when the area was deliberately flooded to make way for a rural development project, the area has been fully exposed to the Bronze Age sepulcher.

The single-chambered tombs were often used for religious ceremonies. It is as old as 2,000 years older than the Celtic cousin on the Salisbury Plain in England, due to the fact that it happened in the fourth or fifth millennium B.C.

Many of the jagged granite standing stones that were part of the Guadalperal complex are now gone. The menhirs, some as tall as six feet, were used to support a large tumulus or mound of earth and pebbles. The tumulus was dismantled during an excavation led by Hugo Obermaier, a Spanish-German anthropologist.

The dolmen are seen as frozen fragments of history by an Archeologist at the University of Alcal. The past emerged from the water, she said.

Angel Castao, the president of a local cultural association, likened the megalith to a giant eye looking into Spain. He said that the place was a gateway connecting the south and the north of the Iberian Peninsula. One of the few places where it was possible to cross the Tagus River was overlooked. It was important until bridges were built a few centuries ago.

An atmospheric high-pressure system driven by climate change has left parts of the Iberian Peninsula at their driest in 1,200 years. In early August, artificial lakes dropped to 36 percent of capacity, well below the 10-year average of 61 percent. The water level in the Valdecaas is at 28 percent.

This July was the hottest month in Spain in at least 50 years, and dozens of sunken landmarks have recently resurfaced. The abandoned village of Aceredo, which was swamped by a dam in 1992, became visible in February due to the lack of rain. The ruins of a village and bathhouses were caked in dried mud this summer at the Buendia reservoir. When the Sau dam was built in 1965, the Romanesque town of Sant Rom de Sau disappeared from view, but an 11th century Lombard church is still intact. The bell tower is the only thing that pierces the water's surface.

ImageAn elevated view of the ruins of a small village, caked in mud and missing roofs and strewn with debris, which line the edge of a reservoir that reflects the clouds in the sky. In the distance, a bridge crosses the reservoir and mountains line the horizon.
The former village of Aceredo, submerged in 1992 to make way for the Alto Lindoso reservoir.Credit...Carmelo Alen/Agence France-Presse — Getty Images
An elevated view of the ruins of a small village, caked in mud and missing roofs and strewn with debris, which line the edge of a reservoir that reflects the clouds in the sky. In the distance, a bridge crosses the reservoir and mountains line the horizon.
ImageWhat’s left of the La Isabela bathhouses, seen from above, in the drying Buendia reservoir.
What’s left of the La Isabela bathhouses, seen from above, in the drying Buendia reservoir.Credit...Susana Vera/Reuters
What’s left of the La Isabela bathhouses, seen from above, in the drying Buendia reservoir.
ImageA view from directly overhead shows the Guadalperal dolmen and the surrounding circles of stone and earth at the edge of the reservoir. A tiny boat sits at the edge of the shore.
The Guadalperal complex seen from above, showing the ring of quartzite, 117 feet in diameter, surrounding the 144 menhirs.Credit...Silvio Castellanos/Reuters
A view from directly overhead shows the Guadalperal dolmen and the surrounding circles of stone and earth at the edge of the reservoir. A tiny boat sits at the edge of the shore.
ImageThe church of Sant Romà de Sau, which vanished in 1965 when the Sau reservoir was made.
The church of Sant Romà de Sau, which vanished in 1965 when the Sau reservoir was made.Credit...Josep Lago/Agence France-Presse — Getty Images
The church of Sant Romà de Sau, which vanished in 1965 when the Sau reservoir was made.

The ruins of the Dolmen of Guadalperal were found a century ago. The Duke of Alba was a champion of archaeology in Spain and encouraged him to explore the hilltop. The House of Alba had a priest who was also a priest. Guadalperal was owned by the duke's brother.

The dolmen is located in the town of Peraleda de la Mata. The first evidence for agricultural practices and livestock breeding can be found in an Early Neolithic site that was excavated several years ago. Around 5,000 B.C., communities were storing aliments, collecting acorn and harvesting cereals.

There is a stone monument to the dead in the local terrain. It wasn't long before his team dug up the dolmen's entryway, a portal so narrow that it could have been built by giants. A corridor of five feet wide and 69 feet long was used to enter the chamber in which the dead might have been buried. Mr. Castao said that the builders wanted it to be dark and mysterious.

During the dig, there were pots, arrows, bows, axes, flint knives, ceramics, pendants and a hole-puncher made of copper. The researchers did not find any human remains. The crew made sketches of any engravings they found after restoring some of the fallen menhirs.

Dr. Overmaier didn't publish his research on the site. He went into exile in Switzerland at the start of the Spanish Civil War after becoming a citizen of Spain. His notes were adapted into a monograph by two Germans.

ImageA ground-level view of one of the dolmen in the foreground, behind which a tourist wearing a backpack takes a photo. There are several other stones visible, blocking a setting sun.
Tourists visiting the Dolmen of Guadalperal, which can be reached on boats operated by a private firm, although archaeologists discourage visits to the site.Credit...Pierre-Philippe Marcou/Agence France-Presse — Getty Images
A ground-level view of one of the dolmen in the foreground, behind which a tourist wearing a backpack takes a photo. There are several other stones visible, blocking a setting sun.

The publication coincides with a civil engineering scheme that involved the construction of hydroelectric dams. Augustbriga's dolmen and remnants were buried at the bottom of the dam. The 200 Bronze Age and Copper Age sites have been identified by Dr. Bueno and her colleagues.

The second-century A.D. temple, known as Los Mrmoles, was dismantled stone by stone and reassembled four miles away. The inhabitants of the 20th century were relocated as well.

The Dolmen of Guadalperal has reappeared every July and September since it reappeared in the summer of 2019. Mr. Castao and Races de Peraleda support a petition to have the megaliths moved to a new location. The preservation of the dolmen is at risk due to the combination of climate change and electricity policies.

The exposed monument is also at risk of being attacked by tourists, who use their phones and selfies to reach the site. The presence of humans on the site is bad. The dolmen's supports were almost without a base because of the decrease in the sediments caused by the trampling of visitors.

Mr. Castao is worried that the menhir could be damaged at the entrance to the burial vault. There is a shape on one side of the slab and a shape on the other side. Mr. Castao believes that the shape of the Tagus was depicted before the dam was built. He said that the crook in the squiggle is related to a bend in the river. The menhir may be the oldest realistic map in the world if the curvy line is true.

The doctor demurred. She said that the tendency for perception to impose a meaningful interpretation on an ambiguous visual pattern is the basis of the hypothesis of a map. The ziggurat is similar to the ziggurat found in megalithic art.

She said it was a snake.