Poson is a Buddhist festival. It is  held on June month. It is very Important day. That grate day Arhath Mahinda arrived. Arhath Mahinda arrive

d to Mihinthala rock. At that time, king Dewanampiyathissa  grate the king was going on deer hunt. Arhath Mahinda preached sermon to the king at the foot of Mihinthala rock. the king became a buddhists. Hot only that sri lankans became Buddhists.