ANCIENT stone crosses and other valuable granite structures on Dartmoor are being electronically tagged in an attempt to discourage thieves.
The move by Dartmoor National Park Authority follows a number of thefts over the last few years, as granite items have become more desirable.
Rice-sized microchips have been hidden in tiny crevices in more than 50 artefacts on Dartmoor, an area which has 150 stone crosses alone, plus numerous granite troughs, apple crushers, wayside and boundary stones.
DNPA archaeologist Jane Marchand said the aim was to tag every vulnerable granite structure.
'They have become very saleable items and can fetch a high price on the black market,' she said.
'We had to find a suitable way of tagging which would be non-intrusive and not destroy the historical integrity of these structures,' she said.
The tiny microchips are secured in place with epoxy resin mixed with some granite dust.
They are completely invisible and the numbers can only be read using a microchip reader. Each number is recorded along with details of the cross and this information will be held by DNPA.
Among the stone crosses which have already been tagged are three at Burrator which are in the keeping of South West Water.
Senior estates surveyor for the company Michael Green said: 'For many years there has been a slow attrition of stolen granite troughs from the Burrator area in particular, so extending this scheme to other moveable granite artefacts will be extremely helpful.
'The moor is a vast place but hopefully, if any monuments are stolen, they can be traced.'