Archaeologists have discovered a unique set of ruins, estimated to date from the eighth century, in the steppes of eastern Mongolia.

The site consists of a sarcophagus surrounded by a square of 14 large, stone pillars covered in Turkic runic inscriptions. The pillars are some of the largest found in Mongolia.

The runes suggest the sarcophagus belonged to a viceroy, or right-hand man, of Bilge Qaghan, who ruled the Second Turkic Qaghanate – a nomadic confederation or steppe empire – between 716 and 734AD. Qaghan is an ancient Turkic title equivalent to the rank of emperor.

This viceroy - or Yabgu - eventually rose up the ranks to become a commander in chief and highest administrative officer during the reign of Bilge's successor, Tengri Qaghan (734-741).

It was previously thought that ruins belonging to Turkic elites were found only in the western part of Ulan Bator, the capital of Mongolia.

But excavations conducted by researchers from Osaka University and the Institute of History and Archaeology of the Mongolian Academy of Sciences have disproved that theory and challenged the accepted history of the region.

Their findings suggest that the Dongoin Shiree steppe, where the sarcophagus lies, was at the centre of the eastern part of the Turkic Qaghanate. The inscriptions shine new light on how power was structured in eastern Mongolia 1,400 years ago, the researchers say.

"This monument will reveal that power relationships of rulers in the east area of the Turkic Qaghanate and their territories as well as their political and military relationships with Mongolian tribes, such as the Khitan, Tatabi, and Tatar," lead author Takashi Osawa said.

"In addition, the arrangement of these stone pillars on the plateau will also provide important information for discussing the religious ideas and world outlook of the ancient nomads," he said.

The Turkic people - a collection of ethno-linguistic groups who speak Turkic languages - emerged in a region extending from Central Asia to Siberia in what is now mostly China. Today, they are spread across central, eastern, northern and western Asia as well as parts of Europe and North Africa.