Birr Castle, as it exists today, is largely an eighteenth- to nineteenth-century structure designed by the architect John Johnson. The ‘castle’ was built around the core of an earlier structure or gatehouse. The site of the current Birr Castle is located only 20-30m from the thirteenth- or fourteenth-century O’Carroll’s ‘Black Castle’, as well as, potentially, the twelfth-century Anglo-Norman motte-castle. Historically, the Black Castle is mentioned in Laurence Parsons 1620s accounts and is illustrated as a rectangular building located on a map dating to 1691.

This map (held in the archives of Worcester College, with a copy in the Birr Castle archives) was commissioned after the battle of the Boyne, as part of a broader initiative to record British defences. The map shows the Black Castle on the edge of a steep cliff edge overlooking the Camcor River as two of six buildings, which form a defensive enclosure; the two buildings are clearly identified as ‘old castles’. The second and largest of these structures is consistent in size with a hall house, and is set within a small bawn, with a square turret at its southeast corner. A square building, to the west of the defensive enclosure, is consistent in size with a medieval tower house and it is likely that one or both structures represent the original Black Castle.

The site around the Black Castle was extensively remodelled in the 17th- and (most notably) the 18th- and early 19th-centuries when the current castle was constructed and orientated to face the demesne rather than the town. The Black Castle is recorded as having been demolished in c. 1778 during this period of remodelling, with accounts from the 2nd Earl of Rosse (end of 18th-century) recalling the Black Castle being pulled down when he was a child; previous to that his father used the castle ‘of a summers evening to drink a glass of wine’. However, the motte and some of the earlier buildings seem may have remained on site past this period.

The ‘site of’ the Black Castle is shown on both the First Edition Map (1838) and the 25” map (1909); the latter of these is a little more specific in pin-pointing a location for the Black Castle within the 19th-century star-shaped fort. However, it is unlikely this landscaping would have removed the medieval buildings in their totality, based on their scale indicated by the 1691 map. Cooke, in the later 19th century, also recorded the site of the Black Castle as c. 70ft from Birr Castle.

Excitingly, during a summer drought in 2018, parch marks, which were interpreted as being associated with the Black Castle, and reported in the Irish Times newspaper, were seen at the supposed Black Castle’s location. Other ‘cropmarks’, such as paths to the telescope, and a possible second moat, within the 19th century star shaped fort, were also visible. The recording of these crop- marks, cartographic records of the site, and, not least, the information held in the Birr Castle Archives and by the Rosse family themselves contributes to a precise identification of the original Black Castle site.