An annual candles festival is celebrated in different parts of Thailand today, but the largest and most important celebration originated and takes place in Ubon Ratchathani in southeast Isaan. It coincides with two events of the Buddhist calendar in the eighth month of the lunar calendar, usually in July: Asalha Puja, which commemorates the date of the Buddha's First Sermon and founding of the Buddhist Sangha; and Khao Phansa, which marks the onset of the rainy season and a three-month period of retreat, loosely referred to in English as "Buddhist Lent," when all monks must remain within their own temple grounds—a stricture that dates back to the time of the Buddha himself, some 2,500 years ago. For the monks, it can be a time of heightened reflection and meditation.