Ballia is an ancient city where great saints and sages of India including Valmiki, Bhrigu, Durvasa,and Jamadagni had their ashrams.
Dadari Mela
An annual fair, the Dadari-Mela, is celebrated on a fairground at the junction of the Ganges and the Ghaghara, on the city's eastern boundary. Regular connectivity with nearby districts as Mau, Azamgarh, Deoria, Ghazipur and Varanasi exists by means of Railway and Roadways. It is world's largest cattle fair. I never had a chance to visit the mela, but it is in the list of places that I have to visit.
The Mela is held at Dadri, which is 5 km. from Balia town. Starting from 'Kartik Purnima' in the months of October-November, the two -week long fair is an amalgam of people from far and close to who come to buy and sell cattle.
http://janatanews.com/2009/may/ballia.php