Celtic spirituality places great importance on the concept of "thin places," where the veil between the Creator and creation is thin, allowing God's presence to be more readily felt. Key thin places for Celts included hilltops, forests, wells, and other natural areas. The document discusses the Celtic cross as a symbol used to mark thin places. It describes the evolution of the Celtic cross from pre-Christian symbols incorporating the circle and cross, to the Christian Celtic cross with the four directions representing the four Gospels. The holiness of places and thin places is a core part of Celtic spirituality's emphasis on God's indwelling presence in all of creation.