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Birr Castle. 	Source: William Alexander.

Birr Castle, the Historic Jewel of Ireland’s County Offaly


Ireland is a nation with a rich and far-reaching heritage. From the Iron Age and into the Middle Ages, the country was shaped by numerous historic episodes. With a strong medieval heritage, Ireland is dotted with forts, old towns, and castles. Many are ruined, and only a few are in good condition and still in use. One such monument is Birr Castle, the traditional home of the Earls of Rosse, which is situated in County Offaly. The castle and the family boast a rich history, and are still thriving - after many centuries.

Birr Castle and the Powerful Earls of Rosse

The history of this region of Ireland is very rich. There was a castle present at the site as early as 1170 AD. It was the home of the prominent O’Carroll family, from where they ruled over a small petty kingdom known as the Ely O’Carroll. However, as the centuries passed and the O’Carroll family waned, the castle grounds passed into the hands of a new owner. This was the English-born barrister and nobleman, Sir Lawrence Parsons. He was granted the castle and 1,277 acres of land in 1620. From this point on, the castle’s true story begins.

The first forms of the Birr Castle as it is today were constructed by the English Masons employed by Parsons. The castle was originally known as "Parsonstown" after the family name, and the original structure was likely a more modest fortified house, typical of the time. However, as the family grew in power and prominence, so did the castle. Eventually, the Parsons became the Earls of Rosse, and Birr Castle was their seat - and would remain so to this very day.

The most significant period in Birr Castle's history began in the early 19th century when the third Earl of Rosse, William Parsons, took a keen interest in astronomy. He embarked on an ambitious project to build the world's largest telescope, which would later be known as the "Leviathan of Parsonstown." Completed in 1845, this telescope had a 72-inch (1.8-m) mirror and played a pivotal role in advancing astronomical knowledge.

Under the direction of William Parsons, the telescope was used to make groundbreaking observations, most notably the discovery of the spiral nature of certain galaxies. This discovery challenged prevailing beliefs about the structure of the universe and laid the groundwork for our modern understanding of galaxies. The Whirlpool Galaxy (M51) was one of the galaxies observed and named using this telescope.

Birr Castle Telescope. Credit: William Alexander

Birr Castle Telescope. Credit: William Alexander

Science and Beauty Combined

The Parsons family's contributions were not limited to astronomy. They also played a significant role in the development and improvement of the local community. They supported various infrastructure projects, including roads, bridges, and schools, contributing to the well-being of the people in the surrounding area.

Throughout its history, Birr Castle underwent several architectural changes and renovations. The castle evolved from its original fortified structure into a more elegant Georgian-style residence. The current, 7th Earl of Rosse, Brendan Parsons, made efforts to restore and maintain the castle's historical character while also adapting it to modern needs. The family still lives in the castle, and as such, it is not open to the public.

The castle is situated within a larger estate known as the Birr Castle Demesne. This expansive estate includes not only the castle and gardens but also woodlands, rivers, walking paths, and historic features. Parts of the Demesne are open to the public, and it offers visitors the opportunity to explore nature, history, and science in one place.

Birr Castle Gardens. Credit: William Alexander.

Birr Castle Gardens. Credit: William Alexander.

The Great Law of Birr

The nearby town of Birr was also very important throughout the history of Ireland. It was here that the famed Lex Innocentium (Law of Innocents), also known as the Great Law of Birr, was established, at the Great Synod of Birr in 697 AD. Also known as the Law of Adomnán, it was an ancient legal code and ecclesiastical law attributed to Adomnán, the ninth Abbot of Iona. Adomnán (627-704 AD) was a prominent Irish monk and scholar, best known for his writings and efforts to promote peace and the protection of civilians during times of conflict. The Law of Adomnán is notable for its progressive provisions aimed at safeguarding non-combatants, particularly women and children, during times of warfare. It is yet another part of the rich shared heritage of Birr town and the nearby Birr Castle.

St Adomnán depicted on stained glass window. (Andreas F. Borchert/CC BY-SA 3.0)

St Adomnán depicted on stained glass window. (Andreas F. Borchert/CC BY-SA 3.0)

Birr Castle remains one of the remarkably preserved historic jewels of Ireland. The Earls of Rosse, who live in Birr Castle, have taken great care to preserve its historical and scientific significance. Efforts have been made to maintain the castle, gardens, and telescope, ensuring that future generations can continue to enjoy and learn from this remarkable place.

Overall, Birr Castle stands as a testament to the intersection of science, history, and natural beauty. Its gardens, telescope, and rich heritage make it a must-visit destination for those interested in astronomy, history, and horticulture.

Top image: Birr Castle.   Source: William Alexander.

By Aleksa Vučković


Houlihan, J. W. 2023. The Great Law of Birr. Offaly County Council.

Moore, P. 1971. The Astronomy of Birr Castle. Mitchell Beazley

Unknown. Birr Castle Demesne. Available at:

Aleksa Vučković's picture


I am a published author of over ten historical fiction novels, and I specialize in Slavic linguistics. Always pursuing my passions for writing, history and literature, I strive to deliver a thrilling and captivating read that touches upon history's most... Read More

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