Nobody knows how he got there or how he died.But the human skull of an elderly man unearthed under a block of flats has given archaeologists a tantalising mystery to puzzle over.

Nobody knows how he got there or how he died.

But the human skull of an elderly man unearthed under a block of flats has given archaeologists a tantalising mystery to puzzle over.

The skull, which is more than 500 years old, was revealed during demolition work on the Canon's Walk flats in Thetford on Monday morning.

A driver pulled up the pilings from the old flats and spotted something unusual underneath, and on closer inspection found it was a skull.

Experts say it is a miracle that it survived as the old bone was in a tiny space between the vast footings of an industrial building - on the site even before the flats were built 45 years ago - and an underground electricity cable.

Another interesting clue to help archaeologists date the skull is that buried with it was an animal's jaw bone, thought to be that of a donkey or horse.

Work stopped on the site when the skull was discovered and the area was marked off for two hours as police investigated, said site manager Arthur Capon, of Norwich-based Lovell Partnership.

"The driver pulled up one of the concrete pilings at about 10.30am on Monday. As he dug it out, there the skull was underneath it. It was a surprise, but this does happen a lot.

"We called the police straight away, as we normally do. They made it a scene-of-crime area and contacted an archaeologist."

Police made inquiries to see if it was a burial ground with local historians and Norfolk Landscape Archaeology's Edwin Rose was called in.

Mr Rose, a development control officer and archaeologist, said while there isn't a lot to tell about the skull yet, it is going to a pathologist in the hope its secrets can be unravelled.

"It is more than 500 years old. It is an unusual shape and the teeth are all very worn. It is an old man's skull," he said.

"What is really interesting is that it was buried with an unidentified animal's jawbone. Vikings were usually buried with their horses, others would put a joint of meat to help the dead travel through the afterlife. It could be a donkey's skull. It certainly looks like an equine skull.

"What's more interesting is it was a million-to-one chance that the skull survived.

"On one side there was a huge industrial building standing on that site, with concrete foundations littered in most of that area and the other side there was an electricity cable. It was in a 2ft-square area."

Mr Rose said: "Old skeletons are very common in Thetford.

"When the cathedral was taken to Norwich in about the 11th century, the town declined in size.

"South of the river, where it was still officially Suffolk, there were lots of little ruined churches.

Evidence of a church, thought to be called St John's, was found in the nearby playing field and human remains have been found around Canon's Close and the playing field, said Mr Rose.

Once its secrets are discovered, the skull will be reburied or placed in a museum.