For a considerable time, experts have been aware of the presence of ancient Greek burials concealed beneath the city. However, their accessibility has been limited until recently. Advanced methods now allow researchers to examine the underground without the need for physical excavation.

A 3D view of the site with the four inferred reference points of Chamber 3 shown as green spheres. Credit: Tioukov et al., Scientific Reports 2023

A group of archaeologists has successfully employed muography, a cutting-edge technique, to unveil a concealed chamber within the Neapolis Necropolis located in Naples, Italy.

The research project involved a team of scholars from the University of Naples Federico II, the National Insтιтute of Nuclear Physics (INFN), and the University of Nagoya (Japan), working in collaboration.

Muon tomography surpᴀsses x-ray-based tomography, such as CT scanning, in its ability to penetrate significantly thicker materials. Consequently, it enables imaging through more substantial barriers.

Muon tomography, also known as muography, utilizes cosmic ray muons to create three-dimensional representations of volumes by analyzing the Coulomb scattering data produced by the muons.

Through the implementation of this technology, they have unveiled a hidden secret lying deep beneath the bustling streets of Naples.

Fragments of nearby Greek burial chambers from ancient Neapolis. Credit: Tioukov et al., Scientific Reports 2023

This concealed realm contains the remnants of the ancient Greek settlers who initially inhabited the region and the catacombs where Christians resided during the Roman era, nearly two thousand years ago.

Originally, Neapolis flourished as a significant trading hub in Magna Graecia and the Mediterranean region. However, it eventually became ᴀssimilated into the expanding Roman Republic by approximately 327 BCE.

In their paper, the team stated, “The remnants of the ancient Neapolis, including its structures, roads, aqueducts, and necropolis, constructed by the Greeks during the latter part of the first millennium BCE, are entombed roughly ten meters below the current street level in the city of Naples.”

Among the captivating structures discovered, one of the most intriguing is an inaccessible concealed chamber dating back to the Hellenistic era, which is believed by the researchers to likely house a burial site.

A nuclear emulsion detector in place at 18 meters below the ground surface. Credit: Tioukov et al., Scientific Reports 2023

Valeri Tioukov, the lead author and a researcher at the INFN of Naples, explained, “By analyzing the density of muons arriving at the detector from various directions, we can estimate the density of the material they have traversed.

“We found an excess in the data that can only be explained by the presence of a new burial chamber.”

Giovanni De Lellis from the Federico II University and the National Insтιтute of Nuclear Physics (INFN) of Naples mentioned in a statement, “Our initial challenge was to develop a compact muon detector with precise angular resolution, capable of being transported and deployed in narrow spaces without access to an electrical grid.”

“The detector we have developed is based on the technologies we use in the subnuclear physics experiments at CERN, and at the INFN Gran Sᴀsso National Laboratories, which study the properties of neutrinos and search for dark matter.”

The detector was left operational for several months, effectively capturing approximately 10 million muons, enabling the research team to generate a comprehensive stereoscopic reconstruction.

The findings of their study were published on April 3 in the Scientific Reports journal.

More information: Tioukov, V., Morishima, K., Leggieri, C. et al. (2023). Hidden chamber discovery in the underground Hellenistic necropolis of Neapolis by muography. Sci Rep 13, 5438.