After the great death (Parinirvana) of the Supreme Buddha, his discourses were secured by categorizing them into text of Pitaka and Nikaya in a great convocation, which is called the first Sangayana (the first convocation) of Arahants under the administration of Maha Kkashyapa Arahant Thero. At that time, Buddha’s teachings were categorized into five Nikaya depending on the length of each discourse. The lengthy discourses were grouped into Deegha Nikaya (long part) and medium size discourses into Majjima Nikaya (medium part). In Anguttara Nikaya (numbered), the discourses that were numbered were included. Different parts of Buddha’s teachings (Dhamma) that were compacted and gathered under some main points were grouped into Sanyukta Nikaya, and discourses of small extent into Khuddaka Nikaya. Each of these Nikaya was then assigned to disciples of Arahants to memorize and protect Dhamma for the future generations. Thus, the Deegha Nikaya, Majjima Nikaya, Anguttara Nikaya, and Sanyukta Nikaya were assigned to the disciples of Ananda Arahant Thero, Sariputta Arahant Thero, Anuruddha Arahant Thero, and Maha Kashshyapa Arahant Thero, respectively. Khuddaka Nikaya was memorized by every monk and protected throughout the history.

Buddha’s discourses in this categorized form were then flowed well through each generation for few decades after that first convocation. After words, the second great convocation (the second Sangayana) was performed in Palulup City to remedy the crisis that was arisen based on Wajjiputtaka Monks’ ten prohibited luxury objects. This convocation was done under the administration of Sabbakamie Yasa Arahant Thero who was foreseen as the Bhikkhu to solve this problem of ten prohibited luxury objects by Supreme Buddha with his divine eye when he was alive. This convocation helped the order of Buddha to be survived purely for another long period of time. In three hundred years after the great death of Supreme Buddha, another flourishing period for Buddhism was begun to rise. This was happened in the era of the great Emperor, the King Ashoka of India. After he saw the death of millions of people from his final battle with King Kalinga, he was pretty upset. This was when a seven years old young monk called Niggrodha Arahant Thero helped him to overcome his stress and sadness in his heart. King Ashoka who was impressed by Niggrodha Arahant Thero’s character started to adore Buddhism. He began building eighty four thousand Stupa and temples around India as a devotion to the mass of eighty four thousand teachings of Buddha. As a consequence of the rise of the Order of Buddha, more people found their way to Buddhism and gathered around it. For this reason, there were not enough people to treat and worship other priests of different religions at that time. Finally, they became like beggars. There was nothing else for them to do except to become Buddhist monks. Thus, they had to join the monkhood of Buddhism in hundreds. However, instead of living a life according to Buddha’s teachings, they performed their old rituals and sacrifices inside temples. Like the unchanging specks of a tiger even though the forest it lives is changed, they lived heretical lives in temples wearing Buddhist robs. As a result of this contamination, a group of corrupted monks was formed aside the Aarya Sanga (the untainted group true Bhikkhu) in the Order of Buddha. The virtuous monks began to do their work separately refusing to do Uposatha Kamma (discussion of how Bhikkhus live with respect to their observed precepts) with these corrupted monks. Therefore, the Uposatha Kamma was not performed for seven continuous years. Another convocation was therefore held with the support of King Dharmashoka (King Ashoka was famous by the name Dharmashoka after his great contribution to Buddhism) to purify the order of Buddha from the contaminations of outside believes. This convocation was carried out under the supervision of Moggaliiputta Tissa Arahant Thero, who was the highest priest among the monks at that time. King Dharmashoka sent groups of monks as messengers to spread the teachings of Buddha to other countries around the world after this convocation. Mihindu Arahant Thero’s arrival to Sri Lanka was a result of this great effort.