Archaeologists working along the Capital's tram route reveal some of their underground findings

Nearby, two long leg bones can be seen, half in, half out of the ground. His colleague Robert McMorran is scraping away earth with a small trowel to expose the rest of the body. The pair are part of a 12-strong team who have just completed four months of painstaking work to excavate almost 300 skeletons from the path of the city's trams project.

Tram workers stumbled on what at first appeared to be a centuries-old murder mystery when they discovered the human bones during pipe-moving work in Leith.

It soon became clear that it was not one isolated burial. There were around 290 skeletons lying just outside the churchyard at South Leith Parish Church. Archaeologists believe they are part of a former graveyard, attached to an earlier church on the same site. They have lain undisturbed for more than 500 years, even when what is now Constitution Street was built over them in 1790.

Experts at Headland Archaeology, the city-based firm working with the council on the Constitution Street excavation, believe they could fill in gaps in their knowledge of Leith's history. The huge size of the sample means it will provide an accurate snapshot of life in medieval times.

Sorina Spanou, who is leading the dig, says: "When they prepared the planning they knew this was a very sensitive archaeological zone. The unexpected thing was the density and preservation. We didn't expect to find nearly 300 skeletons. They are in wooden coffins, which are in good enough condition to identify the wood. There are completely articulated skeletons.

"The results of the analysis will be of local and regional importance. We'll be able to analyse the population, their diet, diseases and age when they died, and where they came from. It's a very rare opportunity to find out more about people's lives in 15th and 16th century Leith."

Once each skeleton has been exposed, archaeologists photographed them and recorded details of their exact position. They then carefully placed each one in a wooden box to take back to their office in Jane Street, off Leith Walk.

These will be studied by human remains specialists, known as osteoarchaeologists, as well as soil and wood experts. Initial measurements will determine their height and sex, before selected samples are used for carbon dating and other analysis of the bones.

The archaeologists use tiny trowels, paintbrushes and even wooden and plastic spoons to painstakingly clean earth from the bones. Sorina explains that metal can damage the bones, so wood is preferable for scraping the soil away.

She says: "It's challenging work, but that's what makes it fun. Human remains are a bit different to excavate compared to structures like buildings. With archaeology, you always think you know everything about a period, and then you find something unexpected. We've had a lot of interest from people around here – I think they think we're the Time Team."

Although the team take the work in their stride, Sorina admits to feeling a little saddened when she discovers the remains of a child.

She says: "We found five or six adults buried with a child. We think they were related, and could have been plague victims. There was a hospital near here.

"I do stop and think about them for a moment – I suppose that's human nature. But I think the excavation is justified as it helps us to piece together a story."

As well as bones, they have also discovered fragments of pottery, shroud pins and pieces of textiles, although these are badly decomposed.

They can also make deductions from the type of wooden coffin – oak is more expensive and suggests that the deceased was relatively well-off.

Once the analysis is completed, they will publish the results, together with drawings and photographs. The bodies will then be re-buried at another site.

The tram works may have divided opinion, but they have thrown up some surprising hidden treasures. Just two months ago, workers discovered another burial ground at the junction of Leith Walk and Elm Row.

Archaeologists believe there was a 16th-century Carmelite priory and leper hospital near the site, but had not been able to pinpoint the location before.

In March, tram workers discovered three mysterious underground chambers on Princes Street, thought to date from the 18th century, although their use is still unknown.

John Lawson, curator of archaeology at the city council, said: "This is probably the largest and most significant archaeological excavation of a graveyard site in Edinburgh, and certainly it's the largest excavation of human remains ever undertaken in Leith.

"The discoveries will feed into the results of research from excavations at St Giles' Cathedral and Holyrood Abbey dating from a similar period, helping us to find out much more about the lives of everday Edinburgh people during this time – roughly the late 15th century to around the 17th century."

SHEDDING LIGHT ON THE PAST

ALTHOUGH the history of Edinburgh is well-documented, archaeologists have made several significant finds in recent years.

Experts now believe the site of the Roman fort at Cramond was occupied as long ago as 8500BC. Ancient artifacts were discovered during an excavation last year, meaning it could be one of the oldest inhabited sites in Scotland.

During the revamp of the Grassmarket last year, archaeologists unearthed evidence suggesting humans were there 3,000 years earlier than previously thought.

Headlands Archaeology was recently called in to the National Museum of Scotland. Staff found the remains of 18th century terraced buildings while lowering the floors to create new galleries.

Last year, workers found the remains of a 2,000-year old Roman fort during work on the new water treatment plant at Glencorse.