His elder brother Hugh Roe was a key confederate leader during the Nine Years' War (1593–1603).[5] Cathbarr and his brothers supported Hugh Roe during the war. In 1599 he fought alongside his brothers at the Battle of Curlew Pass, which resulted in a crucial victory for the Irish confederacy. In 1601 he accompanied them on the march to Kinsale in County Cork,[1] where Spanish reinforcements had arrived.[8][9] Cathbarr fought at the Siege of Kinsale[1] where the confederacy faced a crushing defeat.[9] After the battle he returned to Lower Connacht with Rory.[1] Despite attempts to recover the military initiative, the confederacy was severely weakened. Hugh Roe died in September 1602 and Rory surrendered to the Crown at Athlone in December.[6]
In early July 1608, Cathbarr travelled to Ostia, a coastal town fifteen miles west of Rome, in order to "make holiday and take a change of air". He was accompanied by his brother Rory, Hugh O'Neill, 4th Baron Dungannon, and Donal O’Carroll, Vicar General of Killaloe. Unfortunately, the men "all agreed that that particular place [was] one of the worst and most unhealthy for climate in all Italy". Rory died of fever on 28 July 1608.[13] Cathbarr also became ill, and similarly died of fever on 15 September 1608 in Rome.[1][14] He is buried in San Pietro in Montorio.[13]
After Cathbarr's death, Rosa remarried to the Irish soldier Owen Roe O'Neill.[15]
Cathbarr had a son with Rosa named Hugh O'Donnell, who was aged two years and three months at the time of the Flight of the Earls in September 1607. This puts Hugh's birthdate around June 1605.[16] Hugh became a Captain in the Spanish Army, serving in his stepfather's regiment in Flanders. He was killed in 1625 during the Siege of Breda.[17][1]
Cathbarr also had an illegitimate son, named Conn, with another woman. According to Darren McGettigan, Conn was born with six toes on one foot.[1] According to Francis Martin O'Donnell, it was Cathbarr's son Hugh who had six toes on one foot.[18] In 1608 Sir John Davies stated that the O'Donnell family had high hopes for Conn "for they affirm that one of their saints of Tyrconnell hath prophesied that when such a one, being of the sept of O'Donnell, shall be born, he shall drive all the Englishmen out of Ireland". Conn was raised in the household of Lord DeputyHenry Cary, 1st Viscount Falkland.[1] Conn was also raised by Captain Basil Brooke at Donegal Castle.[19] He was later imprisoned in a London prison, and then in 1629 escaped to Flanders alongside his cousins Mary Stuart O'Donnell and Hugh O'Rourke.[1]
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