The walls of Derry are 400 years old and are listed as one of the most historic sites in Ireland.
It's known as the Maiden City because the stones rebuffed all military advances - but now it seems they're in the firing line.
Holes have been made by contractors employed by Derry City Council as part of a works scheme to install lighting in the walls themselves.
It has angered those who cherish the heritage of the City Walls.
"The agreement was that any lights would be inserted in slots that were cut during the previous lighting scheme so that further damage would be minimised," Mark Lusby from the City Walls Heritage Project told UTV.
"But I was astounded to walk down East Wall to see five new slots had been cut, and people overlook little insertions and new bits of the Walls being removed and every time a little bit of the walls is removed we're getting less and less of the historic fabric left."
Among the stones that have been damaged are sandstone blocks that bear grooves made when soldiers sharpened their swords during the Great Siege in 1689.
Environment Minister Alex Attwood has suspended the works scheme.
This row could hardly have happened at a more embarrassing or inconvenient time, with 2013 marking both the City of Culture year and 400th anniversary of the design and construction of the walls.
An investigation will be carried out and Derry City Council says it's working closely with the Northern Ireland Environment Agency on the matter.