Nagoya University discovers ancient burial chambers in Naples using cosmic ray imaging

The ruins of ancient Neapolis consist of buildings, roads, aqueducts, and cemeteries constructed by the Greeks around the late first millennium B.C. These remnants are buried approximately 10 meters beneath the present-day city of Naples, Italy. However, ensuring the safety of buildings and roads is crucial in densely populated areas such as Naples, meaning that archaeological investigations through excavation are extremely challenging.

If underground structures, such as water reservoirs built after the 16th century or air-raid shelters constructed during World War II, intersect with these ruins, the latter may be investigated from the ground surface. One such investigation led to the discovery of two burial chambers of noble individuals from the ancient necropolis dating back to the sixth to third centuries B.C. in the Sanità district of Naples. Several hypotheses suggesting the presence of additional burial chambers in the surrounding area have been made based on recent investigations using 3D measurements of underground remains.

A research group led by Associate Professor Kunihiro Morishima and Designated Assistant Professor Nobuko Kitagawa of the Institute of Materials and Systems for Sustainability at Nagoya University, in collaboration with the University of Naples, has visualized complex underground remains in the urban area of Naples using cosmic-ray imaging. This work led to the team's discovery of new burial chambers from the Greek era. The discovery was published in Scientific Reports.

Cosmic rays were measured using a "nuclear emulsion," which is a photographic film-type detector, is lightweight and extremely compact and also does not require a power source. This makes it suitable for use in harsh environments such as narrow spaces, dust-filled underground ruins and tunnel interiors. The research group has previously reported the discovery of unknown spaces within the pyramid of King Khufu in Egypt using cosmic-ray imaging with this nuclear emulsion.

From March 10 to April 7, 2018, over a period of 28 days, nuclear emulsion plates were horizontally installed in two locations in an underground basement, 18 meters below ground level. The collected plates were developed in Naples and subsequently analyzed separately at Nagoya University and the University of Naples.

The research group conducted simulations of the cosmic-ray images to explore the unknown burial chamber based on the known underground structures by using cosmic-ray observations. Laser scans of all accessible underground structures were performed from the ground surface to create accurate 3D models of the underground spaces.

The unknown burial chamber was explored by comparing and analyzing the cosmic-ray images obtained from the nuclear emulsion plates at Nagoya University and the University of Naples with the simulation results. The analysis revealed an excess region of muons that could not be explained by simply considering underground drainage networks, above-ground structures and ground density variations. The size of the cavity was estimated based on the excess region and its position within the 3D model. Eventually, the cavity was determined to be a new burial chamber measuring approximately 2−3 meters in size, located approximately 10 meters underground.

The research group also identified notable areas along the newly discovered burial chamber that suggest the existence of underground drainage networks and uncharted cavities. These findings demonstrate that cosmic-ray imaging is an extremely effective method for understanding underground structures.

Journal Information
Publication: Scientific Reports
Title: Hidden chamber discovery in the underground Hellenistic necropolis of Neapolis by muography
DOI: 10.1038/s41598-023-32626-0