Periplo Isola Martana Lago di Bolsena

In Europe's largest volcanic lake rises a steep crescent crag that no foot traveler or tourist ferry is permitted to step on. This natural sanctuary sets the stage for the 5° Periplo Isola Martana Lago di Bolsena, an open water swimming race in the fresh water of Lake Bolsena, setting off from the lakeside village of Marta in Lazio, Italy. Setting out from the beach at Marta-Kornoss, competitors take on a 4,500-metre course designed around a true periplo, the ancient nautical term designating the complete circumnavigation of an island or landmass. Swimmers push away from the mainland shallows into deep volcanic water, charting a direct line toward the crescent crag before tracing its perimeter and heading back across the basin to the finish line at Marta.

The crossing is an exhilarating test of pacing and sighting over open freshwater where sighting lines hinge on the towering volcanic rock. Staged in late September by ASD Tuscia Open Water, the event brings together long-distance racing with a spirit of solidarity, welcoming participants who take to the water to support the charity Lega del Filo d'Oro.

Lake Bolsena caldera: underwater eruptions and 100-metre depths

Lake Bolsena is a vast volcano-tectonic depression measuring roughly nineteen kilometres across, formed over 300,000 years ago following the collapse of the ancient Vulsinio volcanic complex. That cataclysmic collapse produced a caldera spanning sixteen kilometres across, whose floor was shaped by explosive activity that blanketed the surrounding hills in extensive tuff deposits. In later millennia, underwater eruptive vents opened across the submerged caldera bed. Isola Martana originated from these submerged eruptions approximately 132,000 years ago, alongside the neighboring island of Bisentina. Their distinct semicircular silhouettes survive because a portion of each volcanic cone eventually collapsed in on itself, leaving behind dramatic crescent contours rising out of the calm blue surface. On the northern flank of Isola Martana, the lake bed falls away dramatically into depths exceeding 100 metres.

Gran Carro pile dwellings and Queen Amalasuntha on Isola Martana

Human life has clustered around these volcanic shores since the late Neolithic period, when communities built stilt villages directly above the lake shallows. Rising in isolated grandeur two kilometres out from the harbor, Isola Martana remains private property and is completely closed to the visiting public. The island is steeped in dark medieval drama as the remote rock where the Ostrogothic queen Amalasuntha was exiled and subsequently murdered by her cousin Theodahad on April 30, 535.

The waterfront of Marta, traditional fishermen and Bolsena eels

The host town of Marta perches on the southern shore at an altitude of 315 metres, resting directly on the volcanic slopes of Monte di Marta. The village is crowned by the remnants of the medieval fortress commissioned by Pope Urban IV around 1260. It is an authentic working lake town whose fishermen still ply the basin in distinctive traditional boats. These local boats are propelled with asymmetric oars, standing upright as the aft oar doubles as a rudder while working the waters for native European eels, a celebrated delicacy recorded as far back as Dante's Purgatory. In midwinter, fierce northern tramontana winds exceeding 80 to 90 km/h can whip the lake into violent frozen waves known locally as lagheggiate, coating shoreside trees and piers in glittering ice stalactites.

Marta lakefront: the fishermen's beach and the view of Martana

The Borgo dei Pescatori in Marta, the district historically settled by fishermen, has a small beach where boats can still be seen coming back from the lake. The lakefront path in Marta runs along long, shaded, tree-lined avenues. Marta also has play areas for children, benches and sheltered small beaches for lying in the sun after a dip in Lake Bolsena. From the top of the 21-metre Clock Tower of Marta the view takes in both Isola Martana and Isola Bisentina. Isola Martana is the smaller of the two islands of Lake Bolsena, covers 10.3 hectares and faces the town of Marta.