In the Mahavamsa, a key Pali historical text, he is recorded as having travelled from “Alasandra” (thought to be Alexandria of the Caucasus, around 150 kilometers north of today's Kabul, or possibly Alexandria of the Arachosians), with 30,000 monks for the dedication ceremony of the Maha Thupa ("Great stupa") at Anuradhapura in Sri Lanka, when it was completed shortly after the death of the Sri Lankan king Dutthagamani Abhaya (r. 161 - 137 BCE).
The Mahamvasa lists the congregations that visited Sri Lanka for the dedication of the Maha Thupa, explaining that:
"From Alasanda the city of the Yonas came the thera (elder) Yona Mahadhammarakkhita with thirty thousand bhikkhus." (Mahavamsa, XXIX)
This reference says a lot about the role of the Greeks in the Buddhist community of that era;Alexandria of the Caucasus or Alexandria of the Arachosians, cities under the control of the Greek king Menander, had a Buddhist monk population of possibly as many as 30,000, indicating a flourishing Buddhist culture under the Greeks.
The head of this Buddhist community was a Greek (Yona) Buddhist elder whose religious name was Mahadhammarakkhita ("Great protector of the Dharma), a fact that illustrates the involvement of Greeks in the development of the Buddhist faith, in the northwestern part of the Indian subcontinent.
They were able to travel freely south as far as Sri Lanka; this is probably evidence of some political stability along the west coast of the Indian subcontinent. It should be noted that during that time, the Shunga Empire was persecuting Buddhists in the East.
It is also separately established through another text, the Milinda Panha, and archeological evidence, that Menander himself ruled a vast empire in northern India, and that he became a Buddhist arhat. According to Buddhist tradition, he was a great benefactor of the Buddhist faith, along with Ashoka or the Kushan Kanishka.