A valuable Roman skull has been stolen from a pit being excavated by archaeologists in Malton.
Thieves removed the relic from the dig site on Old Maltongate during the night of May 9, and two men were later seen behaving suspiciously nearby.
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The dig project aims to uncover more information about Old Malton, which was the site of a Roman fort and industry including pottery kilns. It is being run by the Defence Archaeology Group in conjunction with the University of York, and some of those working on the excavations are injured armed forces veterans.
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The five acres of land behind the Old Lodge Hotel on Old Maltongate have a 2,000-year history, having been the location of Derventio Brigantum before a Norman castle was built on the site.
Excavations have been ongoing since the 1930s, and ITV's Time Team have filmed in the area.
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The skull had been partially covered before it was taken, and police are looking to trace two men who visited the dig two days after the theft, asking questions and taking photographs. They were seen in a small white van with a registration number similar to YO56 UZN.
The crime comes as Historic England warned that parts of Hadrian's Wall in Northumberland are being damaged by 'nighthawk' metal detectorists illegally hunting for ancient treasure.
They have made around 50 holes in the ground near the Brunton Turret section while searching for items such as Roman coins. Using a metal detector at a Scheduled Ancient Monument site is a criminal offence.
However, it is not thought to be practical to install CCTV cameras at the UNESCO World Heritage Site.
Anyone with any information about the Malton skull theft is asked to contact North Yorkshire Police on 101, select option 2 and ask for PC Mark Atkinson.