The month of Esala (July), during which period this annual pageant is usually held, had been considered a month of celebrations and festivity, both among Indians and Sri Lankans. Even from the lifetime of the Buddha in the 6th century BC, the Esala festival was held to commemorate the Buddha's Conception, his Renunciation and the First Sermon. Esala is also considered to be the beginning of the raining season (Vassana) when the monks commence their Retreat. Also, this month is considered to be the period when ritual performances to the protective divinities are held, (eg Pattini puja) as recorded in the text 'Pattini-Halla'. Being considered a 'chaste' month, the period is held sacred for the availability of water, hence prosperity.
Click Here for More Information