A stone coffin discovered at London’s Westminster Abbey more than 150 years ago has long concealed a stubborn mystery. A new analysis now suggests its occupant was likely a medieval monk or abbot who was buried in a Roman sarcophagus originally made for someone else.

Earlier research dated the limestone sarcophagus to around the fourth century. A three line Latin inscription dedicated it “to the memory of Valerius Amandinus,” who was probably an important London resident because of the coffin’s quality, although nothing is known about his life.

The coffin also bears a cross in a late Anglo Saxon style. Carved into its lid, which measures 5.9 feet long, the symbol was likely created at least 600 years after the sarcophagus itself.

That mismatch raised questions about the age and identity of the skeleton, according to Warwick Rodwell, a consultant archaeologist at Westminster Abbey. His analysis indicates that the remains probably belonged to a medieval monk or abbot of Westminster.

Rodwell reported the findings October 20 in the Journal of the British Archaeological Association. The conclusion rests on evidence from the skeleton, the coffin, the carved cross and an unusual burial practice involving lime.

Workers initially discovered the burial at the abbey in 1820. During the excavation, they broke the lid into six pieces, damaged the skull and left the bones piled in disarray, with possible further disturbance by looters while the coffin remained open.

The coffin and its contents were then reburied without being studied or catalogued. It was found again during renovations in 1869 and moved from the abbey’s North Green region to the East Cloister.

Charles Dickens Jr., the eldest son of novelist Charles Dickens, wrote about seeing the sarcophagus at the abbey in 1879, according to the study. It was later taken to the base of the northwest tower, a difficult move that required more than 36 hours because of its weight.

Rodwell learned about the coffin’s history in 2009. When it was scheduled for cleaning and conservation in 2016 before going on display in new abbey galleries, he saw a rare opportunity to reopen the mystery.

“I saw this as an opportunity to take a fresh look at it, and to see what was inside — if anything — after 150 years of being sealed up,” Rodwell told CNN by email. Inside, he found the bones still jumbled together.

The sarcophagus was carved from a single limestone block and measured about 7 feet long, with walls averaging about 4 inches thick. The skeleton was about 90% complete, while the skull had been reconstructed when the coffin was opened in 1869.

Analysis suggested the remains belonged to a man who died between ages 35 and 49. Radiocarbon dating placed him between A.D. 987 and 1052, and his teeth were in good condition.

Some bones showed healed fractures, osteoarthritis and gout. However, researchers found no evidence of a serious disease or injury that might have caused the man’s death.

After removing the skeleton and clearing away soil and rubble, researchers discovered a rectangular patch of lime. The compound was once believed to accelerate decay and trap toxic vapors that were incorrectly associated with disease.

The patch’s shape suggested that the body had first been placed in a rectangular wooden coffin filled with lime, which was then lowered into the Roman sarcophagus. “This had not been suspected, and the timber coffin had totally rotted away,” Rodwell said.

Covering a body in lime was rare during the Middle Ages and was typically reserved for high status burials, according to Rodwell. Combined with the cross, that evidence pointed toward an important man, most likely an abbot of Westminster.

Two historical candidates fit the period: Ælfwig, who served as abbot from A.D. 993 to around 1020, and Wulfnoth, who became abbot in 1020. The study considers Ælfwig the slightly stronger candidate because he was known to have been a Westminster monk before becoming abbot.

“No single clue clinched the matter,” Rodwell said. “It was a case of assembling and weighing all the strands of evidence.”

A reused Roman coffin would not necessarily have diminished the abbot’s burial. Rodwell explained that stone coffins were difficult to obtain during the late Saxon period because the industry that produced them had disappeared, making a secondhand example a valued “prize.”

Dr. Simon Roffey, a reader in medieval archaeology at the University of Winchester in the UK, said more research is needed to explain the reuse of pagan tombs and sarcophagi during the medieval Christian period. Roffey was not involved in the research.

Although Ælfwig is not widely known, Rodwell said the discovery addresses a mystery that has challenged academics since 1869. It also fills a significant gap in the Anglo Saxon history of Westminster Abbey, which he called “the most important church in Britain.”