The Nikini Full Moon is of great significance in the Buddhist calendar. Many significant events took place on Nikini Full Moon day.

Beginning of the Vassana kala or the rainy season of the year, which the Bhikkhus spend in a retreat-particularly in an abode and devote most of their time for the observance of religious practices and preaching the Dhamma to the lay devotees. As sanctioned by the Buddha, the lay devotees attend to the wellbeing of the Bhikkhus. The Buddha spent the first Vassana Kala following his great Enlightenment at the Deer Park in Issipathana.

Under the patronage of king Ajasatta, Maha Kassapa Arahant Thero led the first Dhamma Sanghayana (Convocation) during August at Rajagaha.. Five hundred Arahant Thera’s participated in the convocation, held at Vebhara Rock by the Sathappanni Grotto in Rajagriha, foot of the Rajagahanuvara Rock