Researchers have found that a couple of skeletons known as the Lovers of Modena, because they are holding hands, were both men.
The researchers could not determine the sex of the skeletons when they were found in Italy in 2009 because they were badly preserved.
But a new technique, using the protein on tooth enamel, revealed their sex.
The actual relationship between the skeletons from the 4-6th Century AD remains a mystery.
The researchers say the two adult males were intentionally buried hand-in-hand.
Some of the suggestions for the link between the two skeletons are that they are siblings, cousins or soldiers who died together in battle, study author Federico Lugli told Italy's Rai news site (in Italian).
Researchers suggest that their burial site could have been a war cemetery.
The researchers from Italy's University of Bologna said in Scientific Reports that the findings had profound implications for understanding funeral practices at that time in Italy.