An ancient monument at the centre of the story of Roman's in Britain has been targeted by illegal metal detectorists.

The Roman fort and amphitheatre at Richborough, near Sandwich, has been the scene of so-called 'nighthawking' - when people without permission descend on a piece of land in search of hidden treasures.

English Heritage, which has responsibility for the ancient site, says it is beefing up security to try and prevent detectorists hunting historic artefacts in contravention of the law.

The fort is currently closed to the public while it undergoes a revamp of its visitor attractions ahead of a re-opening next year.

Roy Porter, senior properties curator at English Heritage South, said: "When people illegally metal detect, they are robbing every one of us of our heritage and our understanding of it.

"The artefacts at Richborough are not about monetary value, every item found at the site is a key to unlocking our past.

"Once items are taken in this undisciplined manner their context cannot be recovered and important evidence of those who came before us is lost forever.

"We are having to direct precious charity resources to further strengthen our security..."

"It is even more disappointing that due to these incidents at Richborough we are having to direct precious charity resources to further strengthen our security presence at our site.

"Those are funds that should be used to conserve and look after the great historic sites in our care but instead it is being used to stop criminal activity."

Richborough was occupied throughout the entire duration of the Roman occupation of Britain, from the invasion of AD 43 until the end of Roman rule around AD 410.

Due to its historic significance, it is given the highest level of protection in law as a Scheduled Ancient Monument.

The impressive ruins and vast collection of objects found at Richborough provide an exceptional insight into four centuries of life there during the Roman era in Britain.

English Heritage believes that 'nighthawks' have taken advantage of the site's closure to undertake their criminal activities.

Mark Harrison, head of heritage crime strategy at Historic England, said: "We are working closely with English Heritage and Kent Police to identify the offenders who have caused loss and damage at this ancient site."

Anyone who believes they are witnessing illegal metal detecting should report it by calling 999 if a crime is in progress, or 101 if a suspected crime has taken place but the suspect is no longer at the scene.

Members of the public are warned not to personally confront 'nighthawks' but should gather information and notify the police.