A massive, 1,500-year-old stone complex that may have been built by nomad tribes has been discovered near the eastern shore of the Caspian Sea in Kazakhstan.

The complex contains numerous stone structures sprawled over about 300 acres (120 hectares) of land, or more than 200 American football fields, archaeologists reported recently in the journal Ancient Civilizations from Scythia to Siberia.

"When the area was examined in detail, several types of stone structures were identified," archaeologists Andrey Astafiev, of the Mangistaus State Historical and Cultural Reserve; and Evgeniï Bogdanov, of the Russian Academy of Sciences Siberian Department's Institute of Archaeology and Ethnography, wrote in the journal article. The smallest stone structures are only 13 feet by 13 feet (4 by 4 meters), and the biggest are 112 feet by 79 feet (34 by 24 m). [See Photos of the Massive Stone Structure and Artifacts]

The structures are "made of stone slabs inserted vertically into the ground," the archaeologists wrote. Some of the stones, which look a little like those at Stonehenge, have carvings of weapons and creatures etched into them.

One of the most spectacular finds is the remains of a saddle made partly of silver and covered with images of wild boars, deer and "beasts of prey" that may be lions, Astafiev and Bogdanov wrote in their article. The images were etched in relief, sticking out from the silver background.

"The relief decoration was impressed on the front surface," Astafiev and Bogdanov wrote. The two researchers think ancient artisans designed the images out of leather and glued them onto wooden boards. "Finally, silver plates would have been laid over the shapes and fixed in place," they said.

Stone-complex discovery

In 2010, a man named F. Akhmadulin (as named in the journal article), from a town called Aktau, was using a metal detector in Altÿnkazgan, which is located on the Mangÿshlak Peninsula, near the eastern coast of the Caspian Sea, when he found parts of a silver saddle and other artifacts. Akhmadulin brought the artifacts to Astafiev who works in Aktau. [7 Bizarre Ancient Cultures That History Forgot]

"Most of the territory consists of sagebrush desert," Astafiev and Bogdanov wrote. However, Astafiev found that the desert location where Akhmadulin brought him contained the remains of an undiscovered 120-hectare stone complex. Akhmadulin located the artifacts in one of these stone structures.

"Unfortunately, the socioeconomic situation in the region is not one in which it is easy to engage in archaeological research, and it was not until 2014 that the authors of this article were able to excavate certain features within the site," Astafiev and Bogdanov wrote.

When excavations got underway in 2014, the archaeologists excavated the stone structure where Akhmadulin had found the saddle. They found more saddle parts, along with other artifacts, including two bronze objects that turned out to be the remains of a whip.

Who owned the saddle?

A great deal of work needs to be done to excavate and study the remains of the stone complex, the archaeologists said. "Certain features of the construction and formal details of the [stone] enclosures at Altÿnkazgan allow us to assume that they had been left there by nomad tribes," Astafiev and Bogdanov wrote.

The design and decorations on the silver saddle indicate that it dates to a time when the Roman Empire was collapsing, and a group called the "Huns" were on the move across Asia and Europe, they said. "The advance of the Huns led various ethnic groups in the Eurasian steppes to move from their previous homelands," Astafiev and Bogdanov wrote.

The owner of the saddle was likely a person of considerable wealth and power as the archaeologists found symbols called "tamgas" engraved on the silver saddle above the heads of predators, something that can be "an indication of the privileged status of the saddle's owner." These signs may also be a link "to the clan to which the owner of the tamga belonged," Astafiev and Bogdanov wrote.

It's not exactly clear why the silver saddle was placed in the stone structure, though it may have been created for a ritual purpose or as a burial good, Astafiev and Bogdanov suggested. They found the remains of one skeleton buried beneath the stone structure; however, the skeleton may date to centuries after the silver saddle was deposited there.

Research is ongoing, and Bogdanov said the team plans to publish another paper on research into the silver saddle in 2017.

Bogdanov said the team hopes to make the public aware of the newly found site. "I hope that one day there [will be] a film about the archaeological excavations on the Mangÿshlak, about ancient civilizations and modern inhabitants," Bogdanov told Live Science.

Original article on Live Science.