The aftermath of a battle or execution from around the 9th century AD has been discovered by Cambridge University archaeologists and students conducting a training dig as part of the University’s undergraduate degree in archaeology.

The burial pit, found on the outskirts of Cambridge, may date from a time when the area was a “frontier zone” in the conflict between the Saxon-run kingdom of Mercia and the kingdom of East Anglia, which was conquered by the Vikings in around 870 AD (CE).

Unearthed during spring and summer last year, the pit contained the remains of ten individuals based on the number of skulls, including at least one decapitation and a man well over six foot in stature – extremely tall for the time – with a trepanned head.

Unusually, the mass grave held a mix of complete and dismembered remains, including a cluster of skulls without clear accompanying bodies and a “stack of legs”, as well as four complete skeletons, some in positions suggesting they were tied up.

All appear to have been relatively young men flung into the pit without care, leading archaeologists to believe they found the wake of a skirmish or battle, or perhaps a mass execution – or a combination of both. The discovery is showcased in a ‘Digging for Britain’ episode broadcast tonight on BBC Two.

The training excavation, led by Dr Oscar Aldred from the Cambridge Archaeological Unit (CAU), took place at Wandlebury Country Park, famous for its “ringwork”: a series of banks and ditches that mark an Iron Age hillfort constructed a millennium before the Viking era.

Archaeologists say the Iron Age features at Wandlebury – a popular destination for school trips and family days out, located three miles south of Cambridge – would have made it a renowned meeting place in the early medieval period just as it is now.

The University’s Department of Archaeology and CAU have worked with local charity Cambridge Past, Present and Future, who own Wandlebury, to conduct student training digs on the site for several years, but this is their most significant and grisly find on the site to date.

“Before we uncovered the first remains, our best find was a 1960s Smarties lid,” said Olivia Courtney, an archaeology undergraduate from Bath, now in her third year at Cambridge University.

“I had never encountered human remains on a dig, and I was struck by how close yet distant these people felt. We were separated by only a few years in age, but over a thousand years in time.”

These are the first human remains found at Wandlebury since 1976, when a storm uprooted a tree close to the recent dig site, and a cache of five skeletons also dating to the same time were uncovered.

Among the most intriguing aspects of the latest find are the complete remains of a man aged between 17 and 24, flung face down into the pit, who would have stood at around 6 foot 5 inches tall.

His height may be down to a growth condition, according to archaeologists, who say he would have towered over others at a time when the average male height was around 5 foot 6 inches.

The man has a large oval hole in his skull, 3cm in diameter, suggesting he underwent trepanation: an ancient surgical procedure in which a hole is bored through a living human’s skull. The hole in the back left side of his skull has signs of healing.

Trepanned skulls have been found the world over, including in ancient Greek and Roman remains. Trepanning was thought to relieve symptoms of conditions such as migraines and seizures, along with disorders we now know to be psychological.

“The individual may have had a tumour that affected their pituitary gland and caused an excess of growth hormones,” said Dr Trish Biers, curator of the Duckworth Collections at the University of Cambridge, where these remains have been taken for further analysis.

“We can see this in the unique characteristics in the long shafts of their limb bones and elsewhere on the skeleton. Such a condition in the brain would have led to increased pressure in the skull, causing headaches that the trepanning may have been an attempt to alleviate. Not uncommon with head trauma today,” Biers said.

The inclusion of dismembered remains alongside fully articulated bodies is highly unusual even for a mass grave, and has puzzled archaeologists.

While one man was clearly beheaded – evident from chop marks on the jaw – and a few others have traces of trauma consistent with combat, there isn’t enough to suggest those buried at Wandlebury were victims of a battle, say archaeologists.

However, to have severed heads, limbs and other remains – from ribs to pelvises – tossed in a pit, with body parts of the same type stacked together in some cases, piled on top of four dead men, at least one apparently bound, suggests terrible violence and perhaps an execution, according to CAU’s Dr Oscar Aldred.

“Those buried could have been recipients of corporal punishment, and that may be connected to Wandlebury as a sacred or well-known meeting place. It may be that some of the disarticulated body parts had previously been displayed as trophies, and were then gathered up and interred with the executed or otherwise slaughtered individuals,” Aldred said.

“We don’t see much evidence for the deliberate chopping up of some of these body parts, so they may have been in a state of decomposition and literally falling apart when they went into the pit.”

Cambridge in the late 8th century was under the control of Offa, ruler of the kingdom of Mercia, but in the late 9th century (around 874-5 AD), half of the Viking Great Army set up camp close to Cambridge, and sacked the town.

Cambridgeshire was then incorporated into the Viking kingdom of East Anglia, and stayed under Viking control up to the early 10th century as part of the Danelaw agreement.

Initial radiocarbon work dates some bones to around this time, but with no associated grave materials more research is required to establish if these are Saxons or Vikings.

“Cambridgeshire was a frontier zone between Mercia and East Anglia, and the continual wars between Saxons and Vikings as they clashed over territory across many decades,” said Aldred. “We suspect the pit may relate to these conflicts.”

Historic England, who are supporting the excavation and monitor and manage archaeology on protected Scheduled Monuments such as Wandlebury, have commissioned a new geophysical survey of the area that archaeologists hope will reveal more about the site surrounding the burial pit.

Tony Calladine, East of England Regional Director, Historic England, said: “Wandlebury is an important natural and historic resource for the people of Cambridgeshire. The extraordinary discovery there speaks to the story of our nation and the lives of ordinary people living during turbulent times.”

Future work from the Cambridge team will include bone analysis including ancient DNA and isotopic work to investigate health, kinship and ancestral links, which will help to establish if these are Viking remains.

The archaeologists will also attempt “refitting” to see if any dismembered remains can be reconstructed to determine how many people were thrown into the pit.

“I would never have expected to find something like this on a student training dig. It was a shocking contrast to the peaceful site of Wandlebury,” added Grace Grandfield, a Cambridge undergraduate from York who took part in the dig.

“Several of the individuals we uncovered were a similar age to me, and it was a sobering experience to identify ever more disarticulated bones and realise the extent of the suffering that had taken place.”