Built by Henry VIII almost 500 years ago to protect England s southern shores, Sandsfoot Castle found a new purpose in modern times as an Instagram selfie spot.
But authorities have now urgently shut the clifftop Tudor artillery fort for fear it is falling into the sea after cracks emerged in its masonry.
Weymouth Town Council said two vertical cracks were spotted in the internal walls and another especially concerning one above the picture arch.
The decision was taken to fence it off to the public - to the likely dismay of the throngs of Instagrammers who take pictures beside the ruins with the picturesque backdrop of Portland Harbour.