The annual Sonepur Mela, one of Asia's largest and oldest cattle fairs, is held on Kartik Purnima, which generally falls in the month November, at Sonepur, around 30 km from Patna, at the confluence of Ganges and Gandak rivers. The site is regarded as holy by the Hindus and several visitors take a dip at the point of convergence and then offer prayers at the Hariharnath Temple. It is said that at the fair, horses and elephants for emperor Chandragupta Maurya's army used to be bought here.

During the ancient times, cattle traders and buyers used to come from as far as Central Asia. The 14-day fair begins with a puja (ritual) at a temple and devotees always take a bath in the river to mark the auspicious day of Kartik Purnima. Today, the stalls at Sonepur Mela sell everything from garments, furniture and toys to utensils, agricultural implements, jewellery and handicrafts. There are also local musical performances, dances and magic shows to be enjoyed. Also known as Harihar Kshetra Mela, it sees visitors from across Asia.