Illegal excavations 'damage' Hadrian's Wall heritage site
Unlawful excavations along Hadrian's Wall are having a "damaging effect" on North East culture and archaeology, heritage groups have warned.
Known as "nighthawking", illegal metal detecting has been carried out at Steel Rigg and Peel Crags within the Northumberland National Park.
The sites are legally protected as Scheduled Ancient Monuments.
It is a criminal offence to use metal detecting equipment there without authorisation from English Heritage.
Mark Harrison, the group's national crime advisor, said: "The practice of nighthawking, particularly from such important sites as Hadrian's Wall, is an issue that we take very seriously.
"We recognise that the majority of the metal detecting community comply with the laws and regulations relating to the discovery and recovery of objects from the land.
"But just as it is against the law to break into someone's house and steal their possessions, so it is illegal to damage land and steal valuable historical artefacts.
"The objects they are stealing belong to the landowner, in this case the National Trust, and the history they are stealing belongs to all of us."
Eric Wilton, National Trust countryside manager for Hadrian's Wall Country Group which looks after a six-mile stretch of the structure, said: "It is disappointing at a time when archaeologists and legitimate metal detectorists are working together more closely that this incident has occurred.
"The National Trust wants the public to enjoy its many and varied sites, such as these at Steel Rigg and Pele Gap, but cannot tolerate illegal metal detecting that harms the appreciation of our collective heritage."
Northumbria Police said it was "committed to investigating these issues".