Question: mamangam festival was celebrated on the bank of the river
Answer: Māmānkam ( Tamiḻ / Malayāḷam : Māmāngam / Mahāmaham or Māmākam ) was a duodecennial medieval fair held on the bank , and on the dry river - bed , of Pērār ( River Nil̥a , River Ponnani , or Bhāratappuḻa ) at Tirunāvāya , southern India .