I think we've mentioned this one before ... this gives a few more details (especially for those of us who can't seem to get the TV program on it) ... from the Yorkshire Post:

EVEN to experts in ancient mystery, it was a shocking Cold Case File.
The complete skeletons of dozens of men – many of them beheaded – were found buried in a Roman cemetery under Driffield Terrace, near The Mount, York, two years ago.
Most were discovered by York Archaeological Trust during investigations before houses were built in the area.
More were found under a nearby back garden where a patio was to be laid.
From the moment they were found archaeologists knew there was something strange about them.
Removed heads were placed in odd positions – between knees, on chests, or down by feet.
Further investigations revealed they were all men – aged 20-40 – who had been in good health. None was local. Dental examinations confirmed they came from as far afield as Africa, Europe, and the Mediterranean.
Could the men have been decapitated post mortem in a ritual, experts wondered? The dead would often have their heads removed to prevent them returning to haunt the living.
But now a painstaking investigation by a team of experts for the BBC's Timewatch has established that the men were beheaded while still alive.
Martin Stockwell, Field Work Manager for York Archaeological Trust, said 56 skeletons had been recovered from the house-building site, and more than half of them had their heads removed. In the back garden, they found 24 skeletons, 15 decapitated.
Evidence by York based pottery expert Vivien Swan suggested the graves dating from the early third century AD.
Mr Stockwell added: "It looks like a cemetery for some specific purpose. But whether they were gladiators, or early Christians, or troops I doubt we will ever know.
"They were not buried with any particular grave goods.
"One had iron shackles around his ankles, indicating they were prisoners. It was not a mass grave.
"They were individual skeletons in individual plots, and not all in supine positions."
The wounds of those beheaded were terrible.
"It was done very messily in some cases with multiple cuts to the vertebrae and did not look like the precise ritual beheading of Roman cults," he added.
The next theory was the decapitated bodies were casualties of a war being fought at the time by Emperor Septimius Severus against the Scots.
However, bone specialists did not think the injuries were caused by war.
The latest idea – by historian Anthony Birley – is the men were the victims of a blood feud between Emperor Severus's sons, Caracalla and Geta, who both wanted to be Caesar after his death in York in AD211.
Mr Birley, whose brother Robin runs the Vindalanda site on Hadrian's Wall, notes that Roman historian Cassius Dio records that Caracalla went on a killing spree, executing even members of the Royal household including doctors, a chamberlain, and the family tutor.
For the programme, Prof Charlotte Roberts, a leading osteoarchaeologist with many years of experience in analysing human remains, confirmed what Kate Tucker, bone specialist for York Archaeological Trust, already suspected, that the men were executed.
Prof Roberts, based at Durham University, said: "This is an amazing site because there were so many decapitated.
"Usually in a cemetery site you only get one or two.
"It was quite clear from the cuts to the neck, vertebrae, and parts of the skull they seemed to have been beheaded from behind.
"People can have their heads cut off after death but the fact they had been done from behind suggested they were still alive at the time."
She added that the techniques used in the investigation had been similar to those used by forensic scientists on murder victims.
"So it will be a pretty gruesome programme and I expect it will get a lot of viewers," she added.

I wonder if anyone has suggested that this is an example of decimation ...