Even before the birth of Buddhism, Asian ascetics in the ancient times when there were no calendars, made it a practice on full moon days to cease worldly pursuits and engage themselves in religious activities.

The Buddha adopted this practice and from this developed the preaching of the Buddhist texts and commentaries (bana) in monasteries and temples on full moon Poya days. And when the Venerable Arahat Mahinda Thero introduced Buddhism to this country in 247 BC he also introduced the Poya tradition. Following is a brief description of the 12 Poyas in the Buddhist calendar and their significance.

1 Vesak (full moon Poya in May)

The Buddhist calendar begins with the month of Vesak. On Vesak Day, Buddhists world over commemorate the triple anniversary of Sakyamuni Siddhartha Gautama The Buddha. Triple anniversary because The Buddha was born, attained Supreme Enlightenment at the age of thirty five, and after a successful ministry of forty five years attained Parinirvana or passed away on a Vesak (May) full moon Poya Day. It was also on a Vesak full moon Poya Day, in the eighth year of his enlightenment, that The Buddha made his third and final visit to Sri Lanka. On this full moon Poya begins the 2541 year of the Buddha. 

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2 Poson (full moon Poya in June)

It commemorates the introduction of Buddhism to Sri Lanka by Arahat Maha Mahinda (son of King Asoka of India) at Mihintale in the third century B.C. Ven Mahinda established the Dispensation of The Buddha (Buddhasasana) in Sri Lanka.

3 Esala (full moon Poya in July)

Commemorates the deliverance of the first sermon to the five ascetics and setting in motion the Wheel of the Dhamma (Dhammacakka) at Sarnath Benares, India. The essence of this sermon is the explanation of the Four Noble Truths: The Noble Truth of Suffering or dissatisfaction or conflicts (Dukkha), the cause of suffering, the cessation of suffering and the path leading to the cessation of suffering. And The Noble Eight-fold Path:

                                                            Esala perahera

1. Right understanding (Samma Ditthi)

2. Right thoughts (Samma Samkappa)

3. Right speech (Samma Vaca)

4. Right action (Samma Kammanta)

5. Right livelihood (Samma Ajiva)

6. Right effort (Samma Vayama)

7. Right mindfulness (Samma Sati)

8. Right concentration (Samma Samadhi)

From July Poya also commences the three month retreat (vassana) of the Buddhist monks.

4 Nikini (full moon Poya in August)

During the month of August the conducting of the first Dhamma Sangayana (Convocation) is commemorated. This was held three months after the passing away of The Buddha. Five hundred Arahat Theros participated in the convocation which was held over seven months in the cave at the foot of the Rajagahanuvara Vebhara Rock.

5 Binara (full moon Poya in September)

Commemorates The Buddha's visit to heaven to preach to his mother and celestial multitude. Also the commencing of the Bhikkhuni (nun's) Order. Pajapati Gotami approached The Buddha and implored him to establish the Bhikkhuni Order.

6 Vap (full moon Poya in October)

The significant events commemorated during this month are: the conclusion of The BuddhaÕs preaching of the Abhidhamma for three months to his mother in the Heavenly realm (devaloka), King Devanampiyatissa of Sri Lanka sending envoys to King Asoka requesting him to send his daughter Arahat Sanghamitta Theri to Sri Lanka to establish the Bhikkhuni Sasana (Order of Nuns).

7 Il (full moon Poya in November)

Celebrates the obtaining of Vivarana (the assurance of becoming a Buddha) by the Bodhisatta Maitriya and the commissioning of 60 disciples by The Buddha to disperse his teachings. Also the conclusion of the three month retreat (vassana).

8 Unduvap (full moon Poya in December)

Arrival of the Bo-tree sapling. This was brought to Sri Lanka from India by Buddhist Theri Sanghamitta, and it is this very tree that is venerated by Buddhists in Anura-dhapura. It is also the oldest documented tree in the world. Sanghamitta Theri established the Bhikkhuni Sasana (the Order of Nuns).

9 Duruthu (full moon Poya in January)

In honour of Lord Buddha's first visit to Sri Lanka. This visit too took place in the first year of The Buddha's Supreme Enlightenment.

10 Navam (full moon Poya in February)

Celebrates the following events in Buddhist history: Entrance into the order of two leading disciples of The Buddha (Sariputta and Maha Moggalana), The Buddha proclaims for the first time a code of fundamental ethical precepts for the monks. The Buddha announces that within three months His Parinibbana (death) will take place. 11 Medin (full moon Poya in March)

Commemorates the visit of The Buddha to his home to preach to his father King Suddhodana and other relatives and show them the path to enlightenment and final deliverance.

12 Bak (full moon Poya in April)

It commemorates the second visit of The Buddha to Sri Lanka which took place in the fifth year of his Supreme Enlightenment.