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Thomas Fitz Anthony was part of the second influx of eminent Anglo-Norman settlers in Ireland. In all likelihood Fitz Anthony arrived in the train of the powerful William Marshal, Earl of Pembroke,who became Lord of Leinster in right of his wife Isabella, Daughter of Strongbow (Richard De Clare), whom he married in 1189. Fitz Anthony built Grennan, a rare example of a hall-keep Norman castle, Shortly before or after he founded Thomastown C.1210 and his grant to the Priory of Inistioge dates from the same time. The castle is entered from the ground floor which is unusual in substantial three-storey building 19.5m x 12.1 wide with a massive base-batter built to prevent undermining in siege situation. There's a chapel in the south angle and the first floor contained the great hall. The Nore waters would have lapped against its bawn wall which is outwise surrounded by a feep fosse. The keep was set within a suite of timber buildings which have since perished.
With the foundation of Thomastown, Fitz Anthony built the fine feudal fortress, Grennan Castle with a motte and bailey on the Nore's alluvial flood plain. On the death of Geoffery Fitz Robert of Kells, he became seneschal of Leinster in 1211, had custody of County Waterford and was Lord of Decies and Desmond having had a grant of these immense tracts of land from King John at 250 marcs a year. He was dismissed from his exalted position in 1225 through failure to pay the agreed rental and on his death in 1229 was heavily in debt to the crown.
Cromwell entered Thomastown in March 1650 meeting scant resistance; the castle was granted to Anthony Stamp and its previous owner, Thomas Den. was banished to County Clare. Later inhabitants included William Harrison, M.P. for Thomastown in 1692-3 and John Hobson, a Dublin solicitor who was M.P. for Inistioge in 1761-8.
The courtyard wall was vandalized in the early 19th-c and the handsome carved quoin stones from Dundry removed. The walls are remarkably thick-3m at the base-and remnants of the great hall (1st floor) and two floors above are marked by the remaining corbel stones in the wall. Grennan Castle is now in private ownership.
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"Grennan Castle was built by Thomas Fitzanthoney in the 13th Century. Thomas FitzAnthony son-in-law of Strongbow had been granted a large area of land, originally called Ogenti, the land was renamed by Thomas to Grennan. The townland where the castle is located still maintains that name today, however the village which grew up around the castle gradually became known by the name of its founder 'Thomastown'.
Grennan Castle measures 20 metres x 13 metres and stands 20 metres tall, the walls at their base are 2.5 metres thick. The ground floor contains three barrel vaulted chambers with an entrance to the second floor on the south side by a staircase built hidden into the thickness of the wall. At the top of the staircase is just a gaping opening down to the floor below. This opening was originally covered by a trapdoor, hence with the trapdoor raised the castle was almost impenetrable.
The first floor of the castle contained the great hall, and the second floor reached by a flight of steps in the east wall contained the dormitory area.
In 1650 Cromwell’s troops called to the castle. The siege lasted only two days, the garrison marched out leaving all their weapons behind them and promised to never again oppose English rule.
Grennan Castle survived in good repair until the early 1800s.
Today cattle pass freely through holes in the slowly crumbling castle walls." - (
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