Joyce thinks the name may have a Danish origin, but others believe it comes from the Irish word Ardchoch.
The ruins of the castle are situated on high ground on the south side of the Ovoca River, and consist of a ruined and now ivy-clad round tower, which protected the northern angle. This building is broken on the riverside to about 12 feet in height, but on the south side it measures some 46 feet.
About 10 feet from the ground is a pointed doorway, which leads to a stone floor formed by the arch of the lower chamber. Thirty-four stone steps in the thickness of the wall give access to the top of the tower from this platform.
This building is one of similar flanking towers which defended the walls still running south and west, the remains of some of the other turrets having only disappeared during the last century.
A barrack for two companies of soldiers was built near the former site of the castle, and the walls of the latter were incorporated with those enclosing the yard of the new building.
A monastery was founded at Arklow by Theobald FitzWalter, hereditary Lord Butler of Ireland, who also built the castle.
Lord Theobald Walter le Botiller died in the castle in 1285, and was buried in the convent of the Friars Preachers in Arklow, beneath a tomb ornamented with his effigy.
In 1331 the castle was attacked by the O’Tooles, but Lord de Bermingham came to its relief with a small party, and drove the enemy off with considerable loss. The same year, however, the Irish got possession of it by treachery.
The Lord Chief Justice again re-captured it in 1332, with the help of Dublin citizens and the English settlers in Wicklow, so that it was once more in the King’s hands, and at this time it was partly rebuilt.
In 1522-24 Sir Piers Butler was accused of being in league with the O’Mores, and of using the castle of Arklow to rob both by land and sea.