In 1474 Red Hugh O'Donnell and his wife, Nuala O'Brien, founded Donegal's Franciscan friary by the shore south of town. It was accidentally blown up in 1601 by Rory O'Donnell while laying siege to an English garrison, and little remains. Four of its friars, fearing that the arrival of the English meant the end of Celtic culture, chronicled the whole of known Celtic history and mythology from 40 years before the Flood to AD 1618 in The Annals of the Four Masters – still one of the most important sources of early Irish history. The obelisk (1937), in the Diamond, commemorates the work, copies of which are displayed in the National Library in Dublin.