Blackrock Castle, which stands on the River Lee guarding the river entrance to Cork City, has been fortified since about 1582. Although Blackrock Castle is the most complete building of its type in the County of Cork, and one of the city's best known landmarks, it is truly not a castle at all, but a watch tower fortress.

It appears that the citizens of Cork built the original fort, in 1582 to safeguard against the pirates whom, were 'carrying away' the vessels entering the harbour. This was further supported by a petition to the Queen in 1585 stating that Cork had "a fort called Blackrock" which the citizens "maintain with artillery to resist pirates and other invaders".