In the heart of Yemen’s Wadi Hadramaut, a cluster of ancient mud skyscrapers soars above the desert floor—a beacon of mankind’s adaptability to the most formidable of environments.

At the edge of a desolate expanse of desert known as the Empty Quarter, the 16th-century Walled City of Shibam remains the oldest metropolis in the world to use vertical construction. Once a significant caravan stop on the spice and incense route across the southern Arabian plateau, British explorer Freya Stark dubbed the mud city “the Manhattan of the desert” in the 1930s.

Every aspect of Shibam’s design is strategic. Perched upon on a rocky spur and surrounded by a giant flood wadi, its elevated position shields it from flooding while maintaining proximity to its primary source of water and agriculture. The city was built on a rectangular grid behind a fortified wall—a defensive arrangement that protected its inhabitants from rival tribes and offered a high vantage point from which enemies would be seen approaching.

View Images Women gather clover in Shibam. Their peaked straw hats, called madhalla, are designed to keep their heads cool in searing desert temperatures. Photograph by Steve McCurry, Magnum Photos

The mud-brick high-rises, which stretch up to seven stories high, were constructed from the fertile soil surrounding the city. A soil, hay, and water mixture was fashioned into bricks and left to bake in the sun for days. The windowless, ground floors were used for livestock and grain storage, while the uppermost levels typically served as communal floors for socializing. Connective bridges and doors between buildings also provided a means of quick escape—another one of the city’s impressive defensive features.

The structures are constantly threatened by wind, rain, and heat erosion, and require constant upkeep. In 2008, a tropical cyclone flooded Shibam, damaging several structures and threatening to topple its earthen towers.

View Images A man performs maintenance work to preserve Shibam's mud-brick buildings. Photograph by ullstein bild/Getty Images

The city is under manmade threats as well. In 2015, Shibam was added the list of World Heritage in Danger along with two other sites when violent civil war erupted in Yemen, thrusting the country into an ongoing humanitarian catastrophe. Historic buildings sustained significant damage during heavy bombing in Sana’a, and remain at risk from armed conflict.

“In addition to causing terrible human suffering, these attacks are destroying Yemen’s unique cultural heritage, which is the repository of people’s identity, history and memory and an exceptional testimony to the achievements of the Islamic Civilization," Director-General of UNESCO Irina Bokova said in a press release.