James and G.R. Pain designed Blackrock Castle, which was built between 1828 and 1829. The building was completed on 3 March 1829 and is situated three miles east of Cork city. It was used by Cork Corporation for civic functions during the nineteenth century. The Mayor of Cork had been Admiral of the Port since 1627 and Admiralty Courts were held in the castle also. Every third year, on the first of August, the Mayor and other members of the Corporation set out on boats from Blackrock Castle for the ceremony of 'throwing the dart'. When the boats had reached the mouth of Cork Harbour between Power Head and the Cork Head the Mayor threw an arrow about four feet long into the sea. The ceremony symbolised the authority of the Mayor and Cork Corporation over the harbour and has been revived in recent years.
The castle was in private hands for many years but is once again owned by Cork City Council. It has been restored and now houses an observatory, operated by staff from the Cork Institute of Technology, as well as a restaurant.
It is the third structure to stand on the site. The first was built about 1582 'to resist pirates and other invaders' and was reinforced by Mountjoy, the Lord Deputy, in 1604. That castle burnt down in 1722 and was replaced by another which was also destroyed by fire in 1827.
The present castle consists of a large circular tower with crenellated parapets resting on large corbels. It incorporates portions of the walls of the second castle which were strong enough to withstand the impact of cannon balls. On its eastern side it is joined to a cylindrical tower rising several feet above the main structure. At the side of this tower is a watergate leading to a slipway.
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