the diamond obelisk

is located in Donegal Town.  In the early 17th century, four Franciscan friars, fearing that the arrival of the English meant the end of Celtic culture, chronicled the whole of known Celtic history and mythology. Starting 40 years before the biblical flood through AD 1618, The Annals of the Four Masters is one of the most important sources of early Irish history. The obelisk (1937), in The Diamond, commemorates the work; copies are displayed in the National Library in Dublin.

Info courtesy of the lonely planet website