A group of researchers from the National Technical University of Athens has conducted an ambitious geophysical study to unravel the hidden mysteries beneath the Temple of Olympian Zeus, one of the most iconic structures of ancient Greece. The research, driven by the need to restore and preserve this historical heritage, has yielded fascinating results combining archaeology, engineering, and cutting-edge technologies.

The temple stands at the heart of Athens and has witnessed the vicissitudes of history since its construction began in the 6th century BCE. However, centuries of natural wear, earthquakes, and human activity have left their mark on this colossal architectural work.

In response, Greek authorities have undertaken restoration work, including building a heavy metal structure to stabilize the surviving columns. But before beginning these efforts, it was crucial to investigate the site’s subsurface for potential risks or archaeological findings.

Temple Zeus Athens Tanks
a) The Temple of Olympian Zeus, also known as the Columns of the Olympian Zeus, is a former colossal temple in the center of Athens. b) Excavations at the western end of the temple, where the end of a Roman sewer system had been found, revealed a void probably representing an arched water tank. The position of a 3D ERT survey is outlined by a red line and the GPR profiles are denoted with green lines. c) the southern-most arched void after excavation. Credit: G. Apostolopoulos et al.

The study, led by the university’s Applied Geophysics Laboratory, used a combination of advanced geophysical methods such as electrical resistivity tomography (ERT), ground-penetrating radar (GPR), and frequency-domain electromagnetic (FEM) techniques. These tools enabled scientists to explore the subsurface with unprecedented precision.

ERT was used to map underground structures and detect voids or anomalies. One of the most notable discoveries was the identification of large arched voids that were previously part of the Roman sewer system. This system was later adapted by the Greek War of Independence hero, General Makrigiannis, who used these structures as a place of prayer during the conflict against the Ottoman Empire.

Ground-penetrating radar (GPR), in turn, revealed finer details, including a complex system of tanks and arched structures north of the temple. These latter findings appear to be connected to the previously detected voids, suggesting the existence of an intricate drainage system that may have been central to the temple’s original design.

Temple Zeus Athens Tanks
The two arched “caves” of General Makrigiannis with J. Vlachogiannis, the writer of the “Memoirs”, in the foreground, and behind them the top of a column of the Temple of Olympian Zeus (from the old book: «The Memoirs of General Makrigiannis» 1st edition by J. Vlachogiannis where this photo exists). Credit: J. Vlachogiannis

The Temple of Olympian Zeus is much more than a mere architectural monument. Initially built under the rule of the Athenian tyrants, its construction spanned over six centuries, reaching its zenith during the reign of Roman Emperor Hadrian in the 2nd century CE. With 104 columns rising to a height of 17 meters, this temple housed one of the largest cult statues of antiquity.

Despite its grandeur, the temple fell into disuse shortly after its completion and suffered looting and destruction over the centuries. Currently, only fifteen columns remain standing, while one more lies toppled after a storm in 1852. This deterioration has underscored the importance of ongoing research to ensure the site’s stability and preservation.

The temple’s location presents significant geological challenges. Athens is situated in a seismically active region, and earthquakes have left their mark on the monument. According to the study, the surrounding terrain comprises a mix of Athenian schist and diluvial deposits from the now-hidden Ilisos River. The research also detected areas of loose material that could pose structural risks to the remaining columns.

Temple Zeus Athens Tanks
An old aerophotograph showing the Temple of Olympian Zeus with the linear stony drainage structures more visible, as the arrows show, ending at the area where the arc type tanks are. G. Apostolopoulos et al.

Thanks to FEM measurements, researchers were able to identify differences in the texture and compactness of the terrain. In the western part of the temple, for example, less compact material was found, which could explain why additional reinforcements were implemented in the foundations of the columns in this area.

The study has not only provided invaluable information for the engineers responsible for restoration efforts but has also opened new lines of archaeological research. The possibility of excavating and fully exposing the detected system of tanks and drains could shed light on how the ancient Greeks managed water and protected their monuments from erosion and flooding.

The collaboration between geophysicists, archaeologists, and engineers highlights the importance of an interdisciplinary approach to addressing heritage conservation challenges. According to the study’s authors, these methodologies could be applied to other archaeological sites in Greece, where monuments face similar threats.


SOURCES

G. Apostolopoulos, K. Leontarakis, C. Orfanos, S. Karizonis, A multi-proxy geophysical study at the site of the Temple of Olympian Zeus, Athens, Greece, to address and resolve challenging archaeological and engineering issues. Journal of Applied Geophysics, Volume 233, February 2025, 105618. doi.org/10.1016/j.jappgeo.2024.105618


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