Coppeen and its surrounding areas in West Cork hold a wealth of historical sites and monuments of unique archaeological value. The fort of Cahirvagliair is one of these unique sites. It is a bivallate ringfort and was one of the chief residences of the Cineál Laoighaire. It has been suggested that the name comes from the Fort of the Son of Laoighaire 'Cathair Mhac Laoighaire'.

The fort has also been connected through local folklore to one of Ireland’s best known historical figures, Brian Boru. It is believed that Brian was held hostage here when he was a young boy between the ages of 8 and 16 years. It has been suggested that because of its size and the stonework in the entrance, that Cahirvagliair must have been built by someone of great importance and may even have been a royal residence.

Cahirvagliair Fort was taken into state care in 1915, but despite this, the fort is in very poor condition. The fosses and ditches which were restored in 1983 and 84 are now in parts, almost non-existent after being flattened. The internal diameter is 42 meters and the overall diameter is 75 meters.

The entrance is of course the main attraction and this statement was made about the site in The Journal of Irish Archaeology: "It is difficult to find a parallel for this entrance in an earthen ringfort but lintelled entrances do occur in stone forts. Generally these entrances are different from Cahirvagliair in that the gate would not be part of a projecting structure, the stones would not normally be dressed and the passage would not be as long.”