Cappadocia's Underground Cities: Engineering in Volcanic Rock

Eighteen Stories Below the Turkish Steppe

In 1963, a resident of Derinkuyu in central Turkey broke through a wall while renovating his home and discovered a room. That room connected to another. And another. Turkish archaeologists eventually mapped 18 subterranean levels extending 85 meters below ground, with chambers for thousands of people, livestock stables, wine cellars, churches, schools, and water wells — a city hidden entirely beneath the central Anatolian plateau. Derinkuyu is the largest of approximately 200 underground settlements identified in the Cappadocia region, and it likely sheltered up to 20,000 people during periods of invasion or religious persecution.

The region's geology made this possible. Cappadocia sits on deep deposits of ignimbrite — a light, porous volcanic tuff formed from compressed ash flows from the eruptions of Erciyes Dağ (Mount Argaeus) and Hasan Dağ millions of years ago. This material is soft enough to cut with iron tools when freshly exposed, hardens as it oxidizes and dries, and is strong enough in compression to support structures — provided the right tunneling techniques are used. Ancient carvers understood this material intuitively, if not scientifically.

The Structure of Derinkuyu

Derinkuyu's 18 excavated levels span from just below the surface to approximately 85 meters depth. Not all levels served the same function; archaeological analysis reveals a deliberate vertical zoning:

The city could accommodate domestic animals on its upper levels — essential in a real siege scenario. Livestock require ventilation, food, and water, and the Derinkuyu system provided all three. The wine presses and storage rooms indicate the facility was not used only in emergencies; it served as processing infrastructure for the agricultural community above year-round, with the lower levels reserved for crisis occupation.

Ventilation: 52 Shafts, 8 Kilometers of Air

An underground city housing 20,000 people plus livestock produces enormous quantities of carbon dioxide and requires fresh air circulation continuously. Derinkuyu's engineers solved this with 52 ventilation shafts, the deepest of which reach to the bottom levels — approximately 85 meters — with cross-section openings of approximately 40–50 centimeters. Some shafts also served as wells, tapping the water table at depth.

• The ventilation system used natural convection: warm air from human and animal respiration rose and exited through upper shafts while cooler air entered through lower ones
• Shaft positioning was staggered to prevent direct short-circuit airflow that would leave some areas without circulation
• The tuff's inherent porosity also allows limited air diffusion through the rock itself, supplementing shaft ventilation
• Carbon monoxide from cooking fires was managed by positioning cooking areas near main ventilation shafts, with the smoke rising to surface exits

Water supply was independent of surface access — critical during sieges. Wells within the city penetrated to the water table, with the deepest wells reaching 55 meters from the city's lower levels. These wells were deliberately placed where surface forces could not poison them; the shaft from above would not align with any accessible surface location visible to attackers.

Rolling Stone Doors: Engineering Defense

The most dramatic defensive feature of Cappadocian underground cities is the millstone door — circular stone discs, typically 1–1.5 meters in diameter and 30–50 centimeters thick, weighing up to 500 kilograms. These were rolled across tunnel entrances from the inside, blocking passage. An attacking force had no external handle to push against; the stone was moved by an interior pin-hole through which defenders inserted a rod to control the door.

The discs were not quarried tuff — they were harder stone specifically selected for durability and rolling function. Their circular shape allowed a single defender to roll the door into place against an entire attacking force. Once sealed, the only way through was to chip away at the door or the surrounding tuff — either option took days and announced progress to defenders deeper in the city, who could reinforce the blocked section.

• Multiple doors at different tunnel intersections allowed section-by-section defense and retreat
• Narrow tunnel widths (often 60–70 cm) prevented attackers from using weapons effectively — one person at a time could pass, and only crouching
• Dead-end tunnel decoys branched off main corridors, potentially trapping infiltrators

Origins and Timeline

The question of who originally carved the Cappadocian underground cities remains partially unsettled. The Phrygians, who occupied central Anatolia from approximately 1200–700 BCE, are the most commonly cited builders based on historical records and preliminary excavation findings. The Hittites and Bronze Age Anatolian cultures may have used some of the shallower caves. The most intensive occupation and likely the deepest excavations appear to date to the Byzantine Christian period (7th–10th centuries CE), when Arab raids on central Anatolia made the underground cities life-saving refuges for entire village populations.

The Excavated Network

Derinkuyu and the nearby Kaymakli underground city are connected by a tunnel approximately 8–9 kilometers long at a depth of around 40 meters — though this connecting passage has not been fully excavated or verified by independent archaeological survey. What has been confirmed: Kaymakli has at least 8 excavated levels and was likely the largest underground settlement by total volume in the region. The full extent of the network in the Cappadocia region is still being mapped; new discoveries of connected chambers and previously unknown tunnels occurred as recently as 2013 in Nevşehir, when construction for an urban renewal project revealed a previously unknown underground city potentially larger than Derinkuyu.