Wat Phu Luang a Phra Ubosot in construction

A phra ubosot or short called "bot" (Thai: โบสถ์) is a building in a Buddhist Wat. It is the holiest prayer room, also called the "ordination hall" as it is where ordinations take place.
The term ubosot, shortened to bot in Thai colloquial speech, is derived from the Pali term uposathagara, which refers to a hall used for rituals on the upostha days -- the Buddhist Sabbath, which falls four times a month on the full moon, new moon, and eighth day after each.
An ubosot stands within a boundary formed by eight sema stones (Thai: ใบเสมา) which separate the sacred from the profane, and thus differs from a viharn (วิหาร). The sema stones actually stand above and mark the Luk Nimit (Thai: ลูกนิมิต), stone spheres buried at the cardinal points of the compass delineating the sacred area. A ninth stone sphere, usually bigger, is buried below the main Buddha image of the ubosot. Both ubosots and wihans typically house Buddha images. The entrance side of an ubosot faces east. Across from the entrance door at the west end of the interior is the ubosot's largest Buddha statue.
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