DÚN Beag Fort near Slea Head, which dates as far back as 800 B.C., sustained substantial damage during the storms last week and part of the monument, has fallen into the sea.
Dún Beag promontory fort is considered one of the most important archaeological sites on the Dingle Peninsula and a popular tourist attraction.
However, the Office of Public Works (OPW) has now closed access to the site, which has suffered substantial damage.
"For reasons of health and safety, it was decided to close the path leading up to the National Monument immediately," an OPW spokesperson said.
"A locked gate has been erected at the end of the pathway leading to the monument and the entrance to the passage itself has been blocked off."
"This National Monument is now extremely hazardous and people are asked not to attempt to gain access to the site."
A preliminary examination at the site took place early last week and it is hoped that a full assessment of the site will take place within the next few weeks.
"Until this assessment is complete, we cannot comment on whether it will be possible to repair the damage or prevent further erosion," the OPW spokesperson added.
"It is the case that part of the monument has been lost to the sea and can never be replaced. Any decision made in this regard will be made in consultation with the relevant agencies involved in the care of our National Monuments and coastal protection including the Office of Public Works."
A report on the Fort's excavation, 'Archaeological Excavations at Dúnbeg Promontory Fort, Co. Kerry' was published in 1981 – details of which are available from the Department of Arts, Heritage and the Gaeltacht.
The excavation results did not reveal conclusively what the site was used for; it may have been defensive, or used for ritual or even status purposes to show the wealth of a tribe, or it may simply have just been lived in.