The complex of tunnels and buildings described in this article was discovered by Keith W. Jones of the United States Navy and myself in the course of our general exploration of the underground antiquities of the Phlegrean Fields, made with the kind permission of Professor Alfonso de Franciscis, the Superintendent of Antiquities for Campania. They are the subject of a book recently published by myself (In the Footsteps of Orpheus, Hale, London 1967), but in view of their very unusual nature I have gladly accepted an invitation by the Director of the British School to contribute to the Papers a short factual account, together with the plans we made in the course of our survey (fig. 1).

When the terraced structures overlooking the bay and port of Baia were excavated in 1956–58, many tunnel entrances were uncovered. With the exception of the one short tunnel leading to the hot spring at the rear of the so-called Temple of Mercury, and a few obvious drainage ducts, the tunnels are all concentrated in the areas marked III and IV on the plans in the guide book, The Phlegrean Fields by A. Maiuri (3rd ed., 1958).