Bolsena is a town and comune of Italy, in the province of Viterbo in northern Lazio on the eastern shore of Lake Bolsena. It is 10 km (6 mi) north-north west of Montefiascone and 36 km (22 mi) north-west of Viterbo. The ancient Via Cassia, today's highway SR143, follows the lake shore for some distance, passing through Bolsena.