The 13,000-foot borehole into the Campi Flegrei volcanic formation is designed to gauge just how active it is.
The complex of 24 volcanic fissures and craters last erupted in 1538, and recent seismic activity indicates it could be ready to blow again.
Much of Campi Flegrei lies beneath the Bay of Naples, and was believed by ancient Romans to be the home of Vulcan, the god of fire.
It exhibited periods of unrest between 1969 and 1972, as well as between 1982 and 1984.
Italy’s National Institute for Geophysics and Volcanology will use sensors to measure seismic activity and temperature at various depths to determine how unstable the volcanic complex is.
Photo: Instituto Nazionale di Geofisica e Vulcanologia