One of the richest inhabitants of fourth century Roman York, buried in a stone sarcophagus with luxury imports including jewellery made of elephant ivory, a mirror and a blue glass perfume jar, was a woman of black African ancestry, a re-examination of her skeleton has shown.

Now, 16 centuries after her death, her skeleton is helping prove the startling diversity of the society in which she lived.

"We're looking at a population mix which is much closer to contemporary Britain than previous historians had suspected," Hella Eckhardt, senior lecturer at the department of archaeology at Reading University, said. "In the case of York, the Roman population may have had more diverse origins than the city has now."

Eckhardt's work with a team of scientists and archaeologists, funded by the Arts and Humanities Research Council and published today in Antiquity magazine, involved re-examining skeletons excavated over a century ago.

Isotope evidence suggests that up to 20% were probably long distance migrants. Some were African or had African ancestors, including the woman dubbed "the ivory bangle lady", whose bone analysis shows she was brought up in a warmer climate, and whose skull shape suggests mixed ancestry including black features.

The authors point out that Roman North Africa was noted for its mixed populations, with Phoenician, Berber and Mediterranean influences.

"This skull is particularly interesting, because the stone sarcophagus she was buried in, and the richness of the grave goods, means she was a very wealthy woman, absolutely from the top end of York society," Eckhardt said.

"We can't tell if she was independently wealthy, or the wife or daughter of a wealthy man — but the bones show that she was young, between 18 and 23, and healthy with no obvious sign of disease or cause of death."

The ivory bangle lady came from a group of graves excavated in 1901, on what would have been the approaches to the Roman city of Eboracum, modern York. The burials were dated to the second half of the fourth century AD, and many had rich grave goods.

One of the richest was the woman's, buried with her treasures including the jewellery and glass, and a piece of bone carved with an inscription translated as "Hail sister, may you live in God" — suggesting she may have been a Christian.

The most poignant symbol of multi-cultural Britain was her bracelets, one of African ivory, one of Yorkshire jet which probably came from Whitby.

The authors comment: "The case of the 'ivory bangle lady' contradicts assumptions that may derive from more recent historical experience, namely that immigrants are low status and male, and that African invdividuals are likely to have been slaves. Instead, it is clear that both women and children moved across the Empire, often associated with the military."

The skull and her possessions will go on display in a new exhibition at the Yorkshire Museum, opening next summer.