Cosmic rays reveal presence of 2,500-year-old hidden underground Greek settlement

Archaeologists used muography to identify this previously unknown subterranean burial. 
Mrigakshi Dixit
Representative image of catacombs in Naples, Italy.
Representative image of catacombs in Naples, Italy.

Mateescu Mugur/iStock 

A new study has discovered potential Greek settlement remains beneath Naples, Italy. This 2,500-year-old settlement was discovered with the help of cosmic rays and lasers.

The remains belonged to the Greeks and the catacombs of Christians who lived in this area during the Roman era about two millennia ago. 

Temples, a forum, and numerous underground tombs once crowded this area. The area now known as Naples was initially known as Cumae, but it was renamed Neapolis around 650 B.C.

According to the study, researchers have long suspected that ancient Greek burials were hidden beneath this city's streets, but they could not find all of them. 

“A little part of this archaeological treasure is accessible, thanks to the underground structures like water cisterns made since the sixteenth century or bomb shelters build during the Second World War which accidentally cross ancient cultural layers,” noted the research paper published in the journal Scientific Reports.

The use muography technique

Thanks to the latest innovation, the team could now peer beneath the streets without the need for digging. As per the study, this location houses hypogea, or wealthy people's burial chambers, from the Greek Hellenistic period (sixth to third centuries B.C.). It also contains tombs from the later Roman period (from the second to fourth centuries A.D.).

These tombs are nearly 33 feet (10 meters) beneath the streets, thereby making them hard to find earlier. Archaeologists used muography to identify this previously unknown subterranean burial. 

A muon is a subatomic particle, the most fundamental building block of the universe. Muons are said to be similar to electrons but heavier and generated by the cosmic rays in the Earth's atmosphere. These particles can peer through hard structures such as walls and rocks. 

Experts can measure the flux of these particles, i.e., muon particles present in a specific area, over time using the muography technique. As a result, it may be possible to create a 3D image of underground cavities. 

Reportedly, the team placed muon tracking devices about 59 feet (18 m) underground, based on a 19th-century vault, to uncover the unknown burial. The team measured muon flux from this location for 28 days. They also performed a 3D laser scan of previously known structures to compare muon flux. 

The thorough examination revealed that the chamber at the depth was most likely a Hellenistic necropolis. Unfortunately, they could not determine what was contained within this hidden chamber. 

The study is conducted by a research institute called Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, in Naples, Italy.

Study abstract:

We report in this paper the muography of an archaeological site located in the highly populated “Sanità” district in the center of Naples, ten meters below the current street level. Several detectors capable of detecting muons - high energy charged particles produced by cosmic rays in the upper layers of atmosphere - were installed underground at the depth of 18 m, to measure the muon flux over several weeks. By measuring the differential flux with our detectors in a wide angular range, we have produced a radiographic image of the upper layers. Despite the architectural complexity of the site, we have clearly observed the known structures as well as a few unknown ones. One of the observed new structures is compatible with the existence of a hidden, currently inaccessible, burial chamber.

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