Birr Castle

Lore & Background

There has been a castle on the site since 1170, and from the 14th to the 17th centuries the O'Carroll family ruled from here over an area known as 'Ely O'Carroll'. After the death of Sir Charles O'Carroll, Sir Lawrence Parsons was granted Birr Castle and 1,277 acres of land in 1620. He engaged English masons in the construction of a new castle, built not on the site of the O'Carrolls' Black Tower but at its gatehouse, with 'flankers' added diagonally at either side, giving the castle the plan it retains today. During the Irish Rebellion of 1641, William Parsons was besieged at Parsonstown (as Birr was then) by Catholic forces for fifteen months. Later, Laurence Parsons, 2nd Earl of Rosse, heightened and 'Gothicised' the castle in the early 19th century.

Reader's Guide

Birr Castle is significant for its role in the history of astronomy. The great telescope, completed in 1845 by the 3rd Earl of Rosse, was the largest telescope on Earth at the time and remained so until the Hooker Telescope at Mount Wilson Observatory in 1917. It made Birr a focus for astronomical observations, attracting visitors such as Charles Babbage and Prince Imperial. After the 3rd Earl's death, the telescope fell into disrepair; its mirror was taken to the Science Museum in London, and its metal structure was melted down for use in the First World War. The telescope was restored more completely in the late 1990s. In the 21st century, astronomical research returned to Birr with the establishment of the Rosse Observatory, including the Irish station of the LOFAR network (I-LOFAR), which is the westernmost station in that network. The demesne also contains Ireland's Historic Science Centre, the oldest wrought-iron bridge in Ireland, and the world's tallest hedge according to The Guinness Book of Records. In 2025, Birr Castle, along with Dunsink Observatory and Armagh Observatory, was added to the World Heritage Tentative List.

Did You Know?

• The great telescope at Birr, completed in 1845, was the largest telescope on Earth until 1917.
• The castle grounds contain the oldest wrought-iron bridge in Ireland, dating from 1820.
• The walled gardens feature box hedges that are over 300 years old and, according to The Guinness Book of Records, the tallest hedge in the world.
• The darkroom of Mary Parsons, Countess of Rosse, on display in the science museum, is believed to be the oldest surviving example in the world.