Buddhism is central to Lao cultural identity. The national symbol of Laos is the That Luang stupa, a stupa with a pyramidal base capped by the representation of a closed lotus blossom which was built to protect relics of the Buddha. The shrine has been rebuilt several times since being created in the thirteenth century by the Khmer, with the largest expansions by King Setthathirath in the 1500s as part of a nationwide building campaign. Traditionally in Laos males would become novice monks at some point in their lives, giving them the opportunity to gain both an education and religious merit (boun). Laos also has a somewhat unusual belief among Buddhist countries that merit is transferable among people, thus a son or daughter may make merit for a parent by temporarily entering a monastery. Lay persons are expected to feed and care for the monks of their local community, with the morning processions of monks (tak bat) who walk to collect offerings. Monks renounce material possessions and labor, thus the community and the monastery (wat) are bound in a mutually reinforcing relationship. Animism Animist traditions are also very strong in Laos with the belief in traditional spirits being a common cultural tie among the Lao Loum, Lao Theung and Lao Sung although such beliefs are strictly organized according to local traditions. Collectively the Lao belief in spirits is referred to as Satsana Phi. Phi are the spirits of buildings or territories, natural places, or phenomena; they are also ancestral spirits that protect people, or can also include malevolent spirits. The phi which are guardian deities of places, or towns are celebrated at festivals with communal gatherings and offerings of food. Many Lao will have a spirit house on or near their property which is an important folk custom used to ensure balance with the natural and supernatural world. Phi were believed to influence natural phenomena including human illness and so appealing to the phi became an important part of Lao identity and religious health over the millennia. Astrology was a vital part to understanding the natural and spiritual worlds and became an important cultural means to enforce social taboos and customs. Traditionally the Lao Loum also believed that ancient mythical serpents known as ngueak inhabited major waterways, carving out the surrounding countryside and protecting key points along rivers or other bodies of water. The earliest name for the Mekong River