1,500-Plus Kilometers on the Map: The Underground Quarries Beneath Odesa

Beneath the ground in Odesa spreads a network of tunnels left over from cutting stone. They are known as “the Odesa catacombs” (Одеські катакомби). Their total length is often given as “2,500 km,” but this figure is not a measured length.

This article sets out how the tunnels came to be and where the numbers come from, drawing on the Енциклопедія Сучасної України (Encyclopedia of Modern Ukraine, “ESU” below; entry “Odesa Catacombs,” written by T. V. Kril, December 2022), the National Academy of Sciences of Ukraine Institute of History’s Енциклопедія історії України (Encyclopedia of the History of Ukraine, “EIU” below; same-titled entry, written by O. A. Bachynska, 2010), the Canadian Institute of Ukrainian Studies’ Internet Encyclopedia of Ukraine’s (IEU) entry “Odesa,” Odesa National University’s guide to its underground reserve, the draft development strategy the Odesa City Council has published, and the UNESCO World Heritage Centre’s page. This article does not cover how to enter the tunnels or visit them.

The Traces of the Stone That Built the City

According to ESU, the tunnels lie beneath Odesa itself and beneath the surrounding villages of Usatove, Nerubaiske, Ivanivka, and Velykyi Dalnyk, among others. They were formed in the early 19th century, a period when the city was being built at speed (ESU, EIU). Odesa’s founding is covered in our article on Odesa’s beginnings.

The stone quarried was shell limestone, called “rakushniak” (ракушняк) in Ukrainian. ESU states that this stone — a Pontian-stage limestone formed in the ancient Pontic Sea — was mined by digging underground, cutting lines into it with tools such as an “English saw,” prying out blocks with a crowbar, and cutting them into standard-sized blocks for sale. Misshapen waste stone went into walls. EIU states that roughly 95% of the tunnels are traces of quarries that produced building stone.

According to ESU, the tunnels range in depth from 1.5 m to 40 m, with an average cross-section about 1.8 m high and 3.5 m wide. Beneath the shallow layers near the city center (above 10 m deep), there are also separate tunnels dug through a loess-like clay layer. Quarrying within the city was banned in the Soviet era (ESU, EIU; neither gives the year of the ban).

“Catacombs” and “Underground Quarries”

“Catacombs” originally refers to underground burial sites such as those in Rome. ESU states that while the catacombs of Rome or Vienna were places of burial and prayer, Odesa’s tunnels were dug to obtain clay or stone, and to create hiding places or shelters; it presents the view that the name “catacombs” does not reflect the reality, and that “underground quarries” (підземні каменоломні) is more accurate.

The tunnels also have their own distinctive vocabulary. ESU states that the shallow tunnels through the loess-like clay layer were called “miny” (міни), the cut blocks sold as stone were called “shtuka” (штука), and the misshapen waste stone was called “but” (бут).

Whose Figure Is 2,500 km?

The figure for the total length is written differently by different sources.

Both Ukrainian encyclopedias present 2,500 km not as a “measured length” but as an estimate. According to ESU, the tunnels actually recorded and mapped come to just over 1,500 km. Neither encyclopedia states who produced the estimate, or when. The draft development strategy the Odesa City Council publishes (through 2027) puts the total length of tunnels formed by shell-limestone quarrying at “up to 3 thousand km,” but it too gives no source for the figure.

The Phrase “World’s Largest Underground Maze”

Some writing introduces Odesa’s tunnels as “the world’s largest underground maze.” None of the three encyclopedias cited here gives a ranking comparing them against the world or Europe. The Odesa City draft development strategy calls the tunnels “one of the largest in the world,” but does not state what was compared against what. What ESU compares is not length, but the difference in how the tunnels came to exist, versus the catacombs of Rome or Vienna.

A Natural Monument, and the University’s Underground Reserve

Part of the tunnel network has been designated a state natural monument. According to ESU, the tunnels beneath Odesa’s Malynivskyi district, at a depth of roughly 15 m, together with the karst cave “Zapovidna,” which preserves Pliocene animal fossils, have since 1963 been the nationally significant geological natural monument “Odesa Catacombs” (4.67 ha), used by Odesa National University. ESU also states that other parts of the tunnels have been designated locally significant historical, scientific, or technical monuments. Ukraine’s reserves and natural monuments more broadly are covered in our article on nature reserves.

A Timeline of the Fossil Cave

According to the university’s guide, the cave has so far yielded more than 50,000 animal bones representing 46 species — mastodons, Etruscan rhinoceroses, two species of saber-toothed cat, one-humped camels, and large ostriches, among others.

Effects on the Ground and Buildings

The tunnels also bear on the city’s ground itself. ESU states that when water seeps into the rock above a tunnel, or when a tunnel floods, the process by which limestone dissolves and soil is carried away intensifies, causing the ground to subside or collapse, which often warps buildings. Collapses occur most readily where tunnels lie shallow, no deeper than 4 m. EIU likewise states that the existence of the quarries has come to cause ground subsidence and building collapse. ESU also points out that proximity to Romania’s Vrancea seismic region, with its relatively frequent earthquakes, heightens the risk of collapse.

The Odesa City draft development strategy likewise states that the tunnels’ condition has worsened over recent decades as they have aged and the load on the city above has grown. The draft sets a target for reinforcing tunnels and “miny” beneath housing, raising the volume from 1,558 cubic meters a year in 2025 to 2,000 cubic meters a year by 2027.

During the Second World War

During the Second World War, the tunnels became hiding places for Soviet partisans resisting the Romanian occupation, and according to EIU, many of them were arrested and executed (ESU, EIU).

Beneath a World Heritage City

According to the UNESCO World Heritage Centre’s page, Odesa’s historic center was inscribed on the World Heritage List and the List of World Heritage in Danger in 2023. That background is covered in our article on Ukrainian cities and World Heritage, and the city’s opera house in our article on the Odesa Opera House. The city’s streets above ground and the tunnels quarried below it are two faces of the same 19th-century construction.