Archaeologists at the Museum of London have found a scrap of treasure missed by tomb raiders who broke into a Roman sarcophagus 300 years ago.

Facebook Twitter Pinterest A human skull under inspection. Photograph: Museum of London

The experts sieved the clay, which had gradually filled the coffin, to retrieve every fragment of evidence about the burial. They found a single flake of gold, possibly from an earring, and a jasper cameo, which was already an antique when the woman died in the first century AD.

The intact sarcophagus, found last year in excavation of a Roman cemetery in Southwark, south London, before building work, was of international importance and only the third scientifically excavated in the capital in modern times.

It will go on display for the first time at an exhibition opening on Friday at the Museum of London Docklands, where the woman lies surrounded by dozens of Roman dead and the objects buried or cremated with them, including jewellery, toys, containers of food and wine and, in one grave, a chicken carcass.

Facebook Twitter Pinterest A gold ring with a gemstone depicting two mice eating together. Photograph: Museum of London

The most enigmatic discovery was an animal skeleton – a tiny dog buried near a child, but in its own carefully dug grave. It had a costly beaded collar with a beautiful sickle moon pendant – but the animal’s head and paws had been cut off.

The Museum of London curator and archaeologist Jackie Keily said: “It meant something to them – but what? Often we’re left with more questions than answers.”

Many were found in recent decades; others excavated long ago were scientifically analysed for the first time.

Facebook Twitter Pinterest Museum of London curators Jackie Keily (left) and Rebecca Redfern examine human bones found in a Roman urn. Photograph: Alicia Canter/The Guardian

The research revealed one woman was of black African origin, and a tall heavy-boned man thought to be German was actually a Londoner whose heavy fancy belt buckle suggests he was a Roman legionary. He was one of many men whose bones bore the scuffs and scars of healed injuries.

A teenage boy, buried with the tiny bodies of a baby and a four-year-old, probably his siblings, was brought up in the Mediterranean. One of the bodies by his side showed early signs of rickets, which the archaeologists believe could have been caused by importing the Roman custom of swaddling infants in yards of cloth, blocking them from having their vitamin D levels topped up by sunlight.

The three are suspected to have all died from an infection, which would have left no mark on their bones.

Facebook Twitter Pinterest Three beakers found with a young woman who had been buried in a wooden coffin. Her body had been placed in a layer of chalk. Photograph: Richard Stroud/Museum of London

The middle-aged woman in Southwark lay quietly in her expensive sarcophagus until the 17th century, when it was probably again an accidental discovery during building work. It had been prised open, cracking the lid carved from a single slab of stone. Her bones had been shoved to one side, her arm torn off and thrown aside, possibly to wrench off a bracelet, and anything buried with her ransacked.

“The sarcophagus with its lid and the clay fill weighed a tonne and a half, and we had to use a very strong lorry to move it. It left us in awe of the Romans who brought the stone from Lincolnshire,” Roy Stephenson, head of archaeology at the museum, said.