A 2,000 year old fort in Port Grenaugh has been left damaged by litter and a fire.
Manx National Heritage says the incident was reported by a member of the public at Cronk ny Merriu.
It says it's not the first time the area has been damaged, after a disposable barbecue left visible scars at the site when it almost sparked a wider fire.
MNH says it's illegal to damage ancient monuments, and is urging people to respect such sites.