Three hillforts, Castlegale, Caherdrinny and Carn Tigherna.are strategically placed in this part of the valley of the river Blackwater. These forts can each be seen one from the other and together may have worked to control access and communication along the valley. All three were investigated by the Discovery Programme, surveyed and the results interrogated by computer.
Castle Gale
This fort is built on an inland promontory, and is somewhat triangular in plan. Before being surveyed by the Discovery Programme, the structural features of the fort could not really be seen due to the rugged terrain and extensive vegetation cover. A detailed three-dimensional survey revealed that the site consisted of two banks with the entrance at the southern side. Steep slopes provide natural defence especially on the north side.
Caherdrinney
Caherdrinney is the largest of the three Blackwater Valley hillforts. Situated at the Western end of the Kilworth mountain range, just to the south of Mitchelstown, Co. Cork, the fort is defined by a single rampart of dumped stone enclosing 13 hectares (31 acres). Detailed survey of the best-preserved sections in 1997 revealed previously unrecorded entranceways and structural details.
Carn Tigherna
The hillfort of Carn Tigherna is built on a steep-sided hill at the eastern end of the Nagles mountain range to the south of Fermoy, Co. Cork. The fort consists of a single rampart of dumped sandstone, irregularly oval in plan, enclosing an area of 3 hectares (8 acres). The Discovery Programme survey, carried out in 1995, revealed additional features such as complex external earthworks and entrances which were previously unrecorded. The summit of the hill is dominated by a Bronze-Age burial cairn, which when opened in the 1830s, was found to contain two burials.