The birth of Siddhartha Gautama, Attainment of Buddha-hood, and
Parinirvana (session of life) all happened in the Vesak Full Moon
Poya (Purnima) day. It is the first full moon of May. That is the
most holy day for Buddhists.
Secondly, the Full Moon day of June is important to Buddhists in
Sri Lanka. The son of Ahoka Empire Mihindu Maha Thero, a Buddhist
Monk came to Sri Lanka and officially introduced Buddhism to Sri
Lanka. The Sri Lankan King Devanampiyatissa became a Buddhist this
day.
Thirdly, the Full Moon day of July is also important to
Buddhists in Sri Lanka. The daughter of Ashoka Empire, Sanghamitta
Maha Teri, a Buddhist nun brought the Jaya Sri Maha Bodhi Tree to
Sri Lanka, a sapling from the Bodhi tree under which Siddhartha
attained the Buddha-hood. That is the oldest known tree still
living in Anuradhapura Sri Lanka.