Bolsena, Lake, whose waters are emptied into the Mediterranean by the little river Marta, is thought to occupy the crater of an extinct volcano. Its waters are beautifully clear, and its shores are crowned with fine oaks, but the malaria prevents all habitation on them. Of two little islands in the lake, one has still the ruins of a little castle where the only daughter of Theodoric the Goth was imprisoned by her husband. The fish of the lake are renowned, and it was the excellence of its eels that caused Pope Martin IV. to be sent by Dante to purgatory.