Lake Bolsena (Italian: Lago di Bolsena) is a crater lake of central Italy, of volcanic origin, which began to collect 370,000 years ago following the formation of a caldera in the Vulsini volcanic complex. Roman historic records indicate activity of the Vulsini volcano occurred as recently as 104 BC; it has been dormant since then. The two islands in the southern part of the lake were formed by underwater eruptions following the collapse that created the caldera.