A sacred grove or sacred woods are any grove of trees of special religious importance to a particular culture. Sacred groves feature in various cultures throughout the world. Examples of sacred groves include the Greco-Roman temenos, the Norse hörgr, and the Celtic nemeton, which was largely but not exclusively associated with Druidic practice.
Mona, now known as Anglesey in Wales, was storied to be the home of the Druids as mentioned in accounts by Julius Ceaser. In AD 60, the Romans under Suetonius Paullinus, decided that it was vital to invade Anglesey and destroy the power of the Druids. The Romans eventually won the battle and destroyed the Druids on Anglesey and cut down their groves of sacred oaks.
Nemetona, or ‘she of the sacred grove’, is a Celtic goddess with roots in northeastern Gaul. She is thought to have been the eponymous deity of the Germano-Celtic people known as the Nemetes. Her name is derived from the Celtic root nemeto-, referring to consecrated religious spaces, particularly sacred groves. She has thus been taken to be a guardian goddess of open-air places of worship.
Sacred Groves and Ravaged Gardens: The Fiction of Eudora Welty, Carson McCullers, and Flannery O'connor (Paperback)