The castle and the surrounding district took their name from Sir Robert Bagod, the Chief Justice of the Irish Common Pleas, who purchased the lands about 1280 and built the castle. From the Bagods, ownership of the castle passed to the Fitzwilliam family, who later held the title Viscount Fitzwilliam. It came into the possession of the influential English-born soldier and statesman Sir Edward Perrers in the early 15th century but later reverted to the Fitzwilliam family. The castle was the scene of a violent conflict in 1441. Sir Edward Perrers' widow Joanna, to whom the castle had passed on their only son's death in 1428, died having appointed James Cornwalsh, the Chief Baron of the Irish Exchequer, as her executor. Cornwalsh took possession of the castle, a move which was greatly resented by Sir Edward Perrers' daughter Ismay who had married into the Fitzwilliam family. Her husband raised a substantial troop of soldiers, attacked the castle, and according to the charges "feloniously murdered" the judge. The charge of murder makes it difficult to explain why Fitzwilliam and Ismay were soon pardoned, although the Government of Henry VI was notoriously willing to issue pardons, even for the most serious of crimes. The castle was described as being in a ruinous condition in 1489 but was later rebuilt and by the 1640s was said to be the strongest fortress near Dublin, although the owners complained of substantial damage to their property in 1642.
Battle of Rathmines
In July 1649 the Irish Royalist leader, James Butler, 1st Duke of Ormonde advanced on Dublin, which was held by Parliamentary forces under Colonel Michael Jones. Anticipating that Ormonde would try to seize Baggotrath Castle, Jones took the precaution of partly destroying it. Nonetheless Ormonde was determined that the castle should be fortified if possible. On 1 August a troop of 1500 men was sent to secure it but, for reasons which have never been clear, they took the whole night to travel a distance of about a mile. When Ormonde himself arrived he found that nothing had been done to fortify the castle. Meanwhile, Jones had been alerted to Ormonde's arrival and attacked the castle with some 5000 men. The Royalist cavalry deserted and most of the foot soldiers were killed or captured, allowing Jones to move on to his decisive victory at Rathmines.
Decay and ruin
No effort seems to have been made by the Fitzwilliams to restore Baggotrath, whose ruins were described in detail by Austin Cooper in 1778, and drawn by Francis Gosse in 1792, some years before what remained of the castle was demolished to allow for the extension of Baggot Street. The name is preserved in Baggotrath Lane, a narrow side street which connects Lower Baggot Street with Merrion Street.
