In Roman times a tiny village of Derinkuyu in Cappadocia region must have hosted a huge population, for a few meters underfoot lies the largest, best- known, and most astonishing underground city of them all, Derinkuyu, eleven levels deep, with 600 entrances, many kilometres of tunnels connecting it to other underground cities, and able accommodate thousands of people. It is truly an underground city, with areas for sleeping, stables for livestock, wells, water tanks, and pits for cooking, ventilation shafts, communal rooms, bathrooms, and tombs. And Derinkuyu is not alone. More than forty complete underground cities and 200 underground structures have been discovered in the Cappadocia, many of them connecting to each other via tunnel. In a past age residents called it Malagobia (Latin, “difficult existence''). It takes its modern name from the town overhead, a Turkish name meaning “deep well'': Derinkuyu.

Mottled grey-brown walls, curving and uneven ceilings low overhead, pillars of rock torturously hand-carved - Derinkuyu looks unassuming, to say the least. You crouch through hatch-like doorways and walk down steep steps seemingly cut as casual afterthoughts. Any given room makes a bland showing for this alleged wonder of the world.

Yet it goes on, and on, and on. One ugly rock room does not excite you, but many dozens, going deeper and ever deeper, carved from almost a square mile of living rock by the sweat of ten thousand brows, do. The cool (10 degree Celsius) air remains fresh, and sometimes, fantastically, you feel a hint of cold breeze. Your excited imagination conjures giant worker ants for this stupendous anthill. From the collective unconscious you synthesize memories of the people who sheltered here: farmers, thin and prematurely aged with hard work. Huge ragtag families, toothless and louse-ridden, but with bright eyes and easy laughter. Arabian horses and diseased oxen munching hay in stone stables. You think of tense times when their owners must have hushed them, while families peered upward in nervous silence, listening to a legion's footsteps.

Before long, passing through weird chambers and down sloping tunnels, you become utterly lost. Red arrow signs point the way farther down, blue arrows upward, and you trust to these like Crusoe trusted Friday. A compass might help, but the rises and plunging spirals still perplex you. Where do you stand in relation to that room you saw five minutes ago? How far below the surface have you come?

Every so often the visitor finds an airshaft, and this answers the second question. These 52 gaping square or circular holes, each wider than a man's height, plunge 55 meters straight down to Derinkuyu's depths. Doorways and windows open onto the shafts at each level. Just under ground level you see the sun above and, below, a vanishing black perspective. Far beneath the surface, on Derinkuyu's seventh and eighth levels, daylight has dwindled to a bright circle the size of a thumbnail. You would see the same view inside a factory smokestack.

Shafts like these provided five vital services: air, light, transport, communication, and water. The shafts brought (and still bring) fresh air everywhere in Derinkuyu, so efficiently that visitors can smoke cigarettes on the eighth level and watch the smoke swirl away toward the nearest shaft. They provide some light, and in ancient times the people may have used shiny metal reflectors to bring the light to their rooms. Many of the shafts have footholds that allow easy climbs between levels. Finally, unlike those of other cities, Derinkuyu's shafts also reached fresh water, giving the city above its ``deep wells,'' its modern name, and (even today) its water supply.

The subterranean cities supposedly began with these shafts. As the first step in enlarging the ancient grain cellars, a city's builders dug straight down, ensuring ventilation before all else. Then the workers dug each level of the city outward from the shafts. The way these workers connected their separate excavations to form each level remains a mystery.

In Deruinkuyu one sees many thick stone wheels; they rest on the ground or stand in notches beside doorways. These wheels, security doors, testify that invaders sometimes discovered Derinkuyu, and that when they did, the residents could defend themselves. They carved each wheel out of the floor of its room, and then drove a hole through its centre. During a battle, a team of men used a wooden pole to roll the wheel down and block the doorway. After those inside withdrew the pole, attackers faced a fearsome task in trying to push back the immense wheel. Meanwhile, besieged residents made spear thrusts through the hole.

Stone wheels guarded the most precious treasures of Derinkuyu's inhabitants. Was it Gold or Jewels? No, although a duck-walk down a long, very low spiralling tunnel leads to a treasure room where one or two guards could hold off an army. Instead, the ancient Christians rolled down those stone wheels to protect their sacred ground.

Here, beyond the barriers, you find a large room with two long stone benches carved straight out of the floor: a seminary. On these benches young missionaries heard the doctrine they would risk their lives to spread. A couple of bedrooms open off the seminary. Nearby, a rounded hole indicates the font where priests baptized the infants of 17 centuries ago, quite possibly ancestors of some readers of this article.

Elsewhere, at the end of a long, scary crawl down a sloping passage, in a part of Derinkuyu that the government has not yet wired for light, you shine your flashlight around a church as big as a basketball court. It seems like a natural cavern, but this area has no caves. To make this underground church, human slaves carried away every rock chip and every speck of gravel by hand.

Several rooms in Derinkuyu remind us of the early importance to Christians of sacramental wine. Some of the wineries near ground level have, or used to have, ceiling holes to the surface. Fresh grapes from the vineyard, poured down the holes, fell into hollows in the rock floor. There people, walked the grapes into pulp. Holes in the bottom of some hollows let the juice flow down into convenient basins in a lower room, ready for the fermenting barrels.

Deep on Derinkuyu's seventh level you find the last and most breathtaking sign of the ancient builders' devotion. Here you enter an enormous 30,5-meter-long hall, a onetime conference room and, some believe, a torture chamber. Two of the hall's three thick columns have candle sconces - or did the residents tie prisoners there? In a nearby room excavators found a grave.

Other rooms open off this hall, including a huge cruciform church 24 meter long and 9 meter wide, with a 3,5-meter ceiling. Some scholars, who believe the entire city predates Christianity, call this room clover-shaped, for the Hittites used the clover as an emblem of state. So far, no one has an idea how this unlikely theory explains the still larger room that opens on the hall's other side. This huge L-shape ends in a short, strange tunnel, tall as a man but barely wide enough to enter, that curves in a tight C from one corner of the room to the adjacent corner.