Dún Ailinne (pronounced [ˈd̪ˠuːn̪ˠ ˈalʲɪ nʲə]; sometimes anglicized Dun Aulin) is an ancient ceremonial site on the hill of Cnoc Ailinne (Knockaulin) in County Kildare, Ireland. It is southwest of Kilcullen, near the N78 road to Athy. It is a large circular enclosure covering most of the hilltop; about 13 hectares.