The earliest Irish name for the site of the modern city was , Old Irish for "oak wood of Calgach", after an unknown pagan. John Keys O'Doherty, the Roman Catholic Bishop of Derry from 1889 to 1907, sought to identify Calgach with Agricola's opponent Calgacus, whereas Patrick Weston Joyce says "Calgach", meaning "fierce warrior", was a common given name. A Celtic Christian monastery was founded at in the sixth century; Adomnán names Saint Columba as founder. The name was changed to "Daire Coluimb Chille", "oak wood of Columba", first mentioned in the Annals of Ulster for 1121. As the monastic site grew in prominence, the name was reduced to just "Doire" (now pronounced ). This was later anglicised to "Derry". In 1604, "Derrie" was granted its first royal charter as a city and county corporate by James I of England. The settlement was destroyed in 1608 by Cahir O'Doherty, Irish chieftain of Inishowen.