# Fathom Castle

- **Country:** Ireland
- **Coordinates:** 54.040100, -6.186300
- **Notes:** Fathom Castle, once a stronghold of the O'Neill clan, was built by Shane O'Neill. Fathom castle was seized during the Nine Years' War and then demolished in 1730 for the construction of a canal.
- **Year Built:** 1550s
- **Castle Type:** Bawn
- **Location Text:** Newry

Fathom Castle, also historically known as Feedom or Fidun Castle, was a significant fortified structure located in Fathom, County Armagh, near Newry in Northern Ireland. Although sometimes associated with County Down due to its proximity to the border, the site served as a strategic stronghold on the western approach to Carlingford. The location originally featured an old castle held by Hugh DeLacy, likely occupied by a knight in his service during the early Norman period. Historical records suggest that Sir Robert Marmion, who arrived in Ireland with Strongbow between 1169 and 1172, was the specific knight responsible for the fortress. His family maintained a prominent presence there for over a century, with descendants documented at the site as late as 1305.

The castle's architectural history evolved significantly during the Gaelic resurgence, which prompted the Marmion family to abandon the forested fort and relocate to the more defensible Carlingford. In the 1550s, the renowned Irish chieftain Shane O'Neill constructed a new structure on the site, utilizing it as a primary residence for the O'Neill dynasty. This iteration of the castle played a pivotal role during the Nine Years War, where it was eventually captured by English forces. Following its military utility, the fortress was demolished in 1730 to facilitate the development of a local canal, erasing the physical structure from the landscape.

Today, Fathom Castle no longer stands, having been completely removed to make way for infrastructure improvements in the eighteenth century. Its historical significance remains tied to its dual heritage as both a Norman holding under the Marmions and a key residence for the O Neills during a turbulent period of Irish history. While the physical ruins are gone, the site is remembered through old maps, including one from 1602 held by the British Library, and local historical accounts that document its transition from a knightly fort to a clan stronghold before its ultimate destruction.

![Photo of Fathom Castle](https://upload.wikimedia.org/wikipedia/commons/2/20/20150704_-_029_-_Flowerpot_Island%2C_Fathom_Five_National_Marine_Park%2C_Ont._-_Castle_Bluff_and_Flowerpot_Island_Light.jpg)

**Source:** https://en.wikipedia.org/wiki/Fathom_Castle (Wikipedia, CC BY-SA)