It was on this day that Emperor Asoka's son, the Arahat Mahinda, officially introduced Buddhism to the island in the 3rd century B.C.

Accordingly, in addition to the normal ritualistic observances undertaken on a Poya day, on Poson day devotees flock to Anuradhapura, the ancient holy capital city of the country, for it was there that Arahat Mahinda converted the then ruler, King Devanampiya Tissa, and his court to Buddhism, thereby setting in motion a series of events that finally made Sri Lanka the home of Theravada Buddhism.

Even today, on Poson Poya, Anuradhapura becomes the center of Buddhist activity. Mihintale, the spot where the momentous encounter between the Elder and the King took place, accordingly receives the reverential attention of the devotees.

The two rituals of pilgrimage and the observance of the Eight Precepts are combined here. Processions commemorative of the event, referred to as Mihindu Peraheras, are held in various parts of the country.

(Source : news.lk)