Khao Pansa marks the beginning of the rains retreat which lasts from the first day of the waning moon of the eighth lunar month to the fifteenth day of the waxing moon of the eleventh lunar month.
First, at the time of the Buddha, monks wandered to propagate the Dhamma throughout the year even during the rainy season. Villagers often saw monks walking in the rain shamefully in their wet dress, walking in mud , slipping and falling .
Sometimes they walked on small animals trying to escape the inondations.It is during the rainy season rice grows , monks walking through the plantations often caused damage to rice plants.
The conduct of monks angry villagers complained to the Buddha. When he was informed of these problems , the Buddha established a rule that monks remain permanently in one place during the rainy season. Therefore, during the rains , the monks stay in the monastery to study Dhamma and practice meditation . They should not spend the night outside .