The ancient Irish swore their oaths by the "Three Realms" – Land, Sea, and Sky. Based on this precedent, reconstructed Gaelic ritual structures acknowledge the Land, Sea and Sky, with the fire of inspiration as a central force that unites the realms. Many Celtic Reconstructionists maintain altars and shrines to their patron spirits and deities, often choosing to place them at outdoor, natural locations such as wells, streams, and special trees. Some CRs practice divination; ogham is a favored method, as are folkloric customs such as the taking of omens from the shapes of clouds or the behavior of birds and animals.