Board, Mike Kay The Frederick County Forestry (17 January 2016). "Building of cairns has long history". The Frederick News-Post (in ஆங்கிலம்). Retrieved 2022-09-20.
worldhistory.org
Mark, Joshua J. "Clava Cairns". World History Encyclopedia (in ஆங்கிலம்). Retrieved 2022-09-20.
