(CNN) - Between 4500 and 2500 BC, the bodies of a couple, believed to be married, were placed carefully side by side in an ancient burial site of the Harappans, one of the world's earliest civilizations.
Thousands of years later, in 2013, a team of Indian and South Korean researchers began excavation work in the necropolis now located in Rakhigarhi -- around 100 miles northwest of India's capital, New Delhi -- in a bid to extract DNA from the skeletal remains.
They discovered dozens of skeletons during the excavation process, which ended three years later. Their finds included the couple, the scientists said in a study published in the peer-reviewed ACB Journal of Anatomy. They believe this is the first Harappan pair confirmed to have been buried together.
"Observation revealed that they died at the same time and they were buried at the same time," said Vasant Shinde, the archeologist who led the team.
The skull of the man was found facing the body of his female partner. "They were intimately placed in the burial," Shinde said. "So we thought maybe they shared [a] very intimate relationship" and were probably husband and wife.
Shrouded in history
Shinde added that the couple must have been married "because, had they been in an illicit relationship, the community would not have [given] them a proper ceremonial burial."
But one major mystery remained: How did these Bronze Age lovebirds die at the same time? Were they wiped out in a plague? Killed in a ritual death? Or did this star-crossed pair take their own lives?
The archeologists couldn't find any trace of disease, nor were there any injury marks to the skeletons that would have suggested they were killed. "Our guess is that probably they may have died of heart failure," Shinde said, before adding that this was just speculation.
In the paper, the scientists ruled out the possibility that the woman, believed to be in her early 20s, took her own life shortly after the death of her husband, who was between 35 and 40 years old.
"The couple's burial ... should not be considered to have been the outcome of any specific funeral customs commonly performed at that time," the study said, referring to a ritual in which a wife would kill herself after the death of her husband. "Rather, it is more plausible that two individuals died at or almost at the same time, and that therefore, they had been buried together in the same grave."
The researchers said more studies of Harappan graves are needed to solve the mystery, "as joint burials are important for inferring historical family structures and the broader society they represent."
Fascination and debate
Archaeologists also found pots in the grave, which would have contained food and water: grave offerings for the dead. One agate bead, "possibly a part of a necklace, was found near the right collar bone" of the male skeleton, they said.
Couple burials like the one in Rakhigarhi have long been a source of fascination and fierce speculation, the scientists added.
In 2007, archeologists excavating a Neolithic burial site in Italy found a couple locked in a tender embrace. It is still a matter of debate how the Lovers of Valdaro, as they came to be known, died.
The same is true of another case in Siberia, where the couple were found facing each other and holding hands.
For now, the team in India will continue extracting DNA from their finds. "Our ultimate goal is to understand the social composition of [the] human population there" and the relationship between the Harappan and contemporary population, Shinde said.
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