Corfe Castle was blown up during the Civil War

The upper section of the medieval Corfe Castle is being fenced off.

The castle, in the Isle of Purbeck, was blown up during the Civil War and most of the ruined structure has remained unchanged since the 17th Century.

The National Trust, which runs the castle, said it had recently found some evidence of crumbling masonry.

It said the upper area, which contains the keep, would be closed but the rest of the castle, including the Outer Bailey and West Bailey, would remain open to visitors.

The ravages of time may be having a temporary effect on part of the castle Pippa Russell, manager

The crumbling has been caused by water freezing and expanding inside the more exposed parts of masonry that are scattered around the keep.

A decision to carry out any remedial work will be taken once English Heritage has inspected the site.

Pippa Russell, visitor and enterprises manager for Corfe Castle, said: "The safety of our visitors is of paramount importance to us and must determine our course of action when faced by a potentially dangerous situation.

"The ravages of time may be having a temporary effect on part of the castle, but we are not anticipating any reduction in the huge appeal of Corfe, especially to families, during the Easter holidays."