Defensive structures on the Owenabue

The Owenabue is a rather small stream that starts just north of Crossbarry and then flows 32 kilometers towards Cork harbour. Until it reaches Carrigaline it is only a small river but just after the bridge in Carrigaline it widens and by the time it reaches Crosshaven it is almost a mile wide. It might seem an insignificant river with no historic and strategic relevance but nothing is further from the truth.