In Yemen, there's a city full of 500 year old skyscrapers made of mud

Shibam, Yemen's "mudbrick Manhattan". Image: Jialiang Gao/peace-on-earth.org/Wikimedia Commons.

Deep in Yemen’s most remote valley lies the city of Shibam. Surrounded by palm groves, and flanked by the steep cliffs leading up to the Yemeni highland on both sides, the city of 2,000 inhabitants hardly seems impressive. Just a handful of high-rise residential buildings, not so different from the Soviet-style blocks found across the Arab world.

Yet  these buildings don’t date from the 20th century, or even the late 19th century. They were built almost five centuries ago, and have remained largely unchanged since.


On a dustless day, the white finish of its walls can be seen from miles away. The city, one of the few to be designated a UNESCO World Heritage site in its entirety, appears to rise from the plains. Its 500 houses reach an astounding 100 feet in height, almost as high as Chicago’s  first skyscrapers. Perhaps most remarkable of all is the fact that the city was built using nothing but mud.

From a historical point of view, this is an incredible piece of engineering. But does the city also hold the key to a more sustainable architecture? Salma Damluji, the world’s foremost expert on Arabia’s traditional architecture, thinks the city’s use of mudbrick – bricks that have been dried in the sun rather than fired – is a key technique developed to cope with challenges posed by the harsh climate.

A close up of the "skyscrapers". Image: Aiman Titi/Wikimedia Commons.

Mudbrick has a higher heat capacity and lower conductivity than concrete, which means it slows the rate at which the temperature within the building changes. It’s also cheap to produce - labour costs are the only real costs involved - and it’s eco-friendly. Not only does the production of sun-dried bricks involve no polluting emissions, the bricks are also reusable.

And, unlike fired bricks, the physical structure of dried bricks does not change during the drying process. Without its white protective layer, a wet brick simply becomes mud.

In Shibam, climatic considerations manifest themselves in more than just the building material. Wooden windows provide privacy, refract glare and promote air circulation with their low placement, and small ventilation holes near the ceiling. Narrow streets and open plazas further enhance this air circulation on a city level. Thus, the architecture of Shibam reveals a complete approach to urban planning, fine-tuned to the city’s climate and social structure.


Although Shibam’s skyline probably forms its pinnacle, mudbrick architecture is widespread in the Middle East. One of its greatest champions was the Egyptian architect and intellectual Hassan Fathy (1900 – 1989), whose architectural philosophy took great inspiration from the socialist politics of Egypt’s anti-colonial hero: Gamal Abdel Nasser.

James Steele, in his biography of the architect, writes that, “On the one hand, Fathy respected and admired European traditions, while on the other hand he resented them as part of a colonial legacy that had threatened Egypt’s identity.”

Spurred on by discomfort with European models of architecture and urban planning, Fathy researched a wide range of architectural traditions native to Egypt. Though he was greatly impressed by both Pharaonic and Islamic monumental architecture, he was more directly influenced by the vernacular architecture of rural Nubia, an area covering the south of Egypt and the north of Sudan.

It was in Nubia where he first encountered mudbrick. “Once convinced of the long history, durability and cultural applicability of mudbrick, as well as its low cost and environmental advantages,” Steele writes, “Fathy saw no reason why it should not be used on a wider scale.”

Towards the end of his life, he was widely recognised for his development of an architectural philosophy that integrated modern technology with the demands of local culture and nature, winning the Aga Khan Award for Architecture in 1980.

And yet it appears that his work failed to make a lasting impact on architecture in the Middle East. No large scale projects involving traditional building methods exist, and even Shibam is under threat.

While decades of political instability and the current war between Houthi rebels and the Saudi-backed government forces have largely passed by the remote valley, Shibam’s architecture has been in decline since the nationalisation of many of its buildings. Although the buildings are rented out to their original owners, a lack of ownership has made their inhabitants reluctant to invest in the considerable maintenance costs. Without regular maintenance, crucial experience with traditional building methods risks being lost forever.

In close up. Image: Jialiang Gao/peace-on-earth.org/Wikimedia Commons.

And local tradition is crucial. When Oxfordshire organic farmers Lutfi and Ruby Radwan, inspired by the mud brick architecture of Saudi Arabia and Senegal, built Willowbrook Farm, they decided to use similarly eco-friendly methods. However, Britain’s climate is, unsurprisingly, not quite dry enough for sundried bricks.

“Instead, we built using the traditional British method of mixing the cob and building up directly in a continuous lump,” Lutfi says. “We admire Hassan Fathy’s work, but it didn’t influence us greatly. More importantly I had visited a number of mud buildings in Britain to see how local issues were dealt with.”

“Mudbrick architecture is more sustainable and cheaper if one factors in the environmental costs,” he continues. “Materials and labour can usually be sourced locally, so it benefits a local economy rather than relying on inputs from outside, which also affects energy costs involved in transportation.

"Plus, its environmental impact is minimal. These traditional methods are certainly a viable alternative to less environmentally sustainable modern methods.”

Sustainable, local architecture. With a shortage of 3.5m affordable homes reported in the Middle East and North Africa, perhaps an affordable, durable and eco-friendly solution lies in the traditions of a forgotten Yemeni valley.

 
 
 
 

To build its emerging “megaregions”, the USA should turn to trains

Under construction: high speed rail in California. Image: Getty.

An extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, out now from Island Press.

A regional transportation system does not become balanced until all its parts are operating effectively. Highways, arterial streets, and local streets are essential, and every megaregion has them, although there is often a big backlog of needed repairs, especially for bridges. Airports for long-distance travel are also recognized as essential, and there are major airports in all the evolving megaregions. Both highways and airports are overloaded at peak periods in the megaregions because of gaps in the rest of the transportation system. Predictions for 2040, when the megaregions will be far more developed than they are today, show that there will be much worse traffic congestion and more airport delays.

What is needed to create a better balance? Passenger rail service that is fast enough to be competitive with driving and with some short airplane trips, commuter rail to major employment centers to take some travelers off highways, and improved local transit systems, especially those that make use of exclusive transit rights-of-way, again to reduce the number of cars on highways and arterial roads. Bicycle paths, sidewalks, and pedestrian paths are also important for reducing car trips in neighborhoods and business centers.

Implementing “fast enough” passenger rail

Long-distance Amtrak trains and commuter rail on conventional, unelectrified tracks are powered by diesel locomotives that can attain a maximum permitted speed of 79 miles per hour, which works out to average operating speeds of 30 to 50 miles per hour. At these speeds, trains are not competitive with driving or even short airline flights.

Trains that can attain 110 miles per hour and can operate at average speeds of 70 miles per hour are fast enough to help balance transportation in megaregions. A trip that takes two to three hours by rail can be competitive with a one-hour flight because of the need to allow an hour and a half or more to get to the boarding area through security, plus the time needed to pick up checked baggage. A two-to-three-hour train trip can be competitive with driving when the distance between destinations is more than two hundred miles – particularly for business travelers who want to sit and work on the train. Of course, the trains also have to be frequent enough, and the traveler’s destination needs to be easily reachable from a train station.

An important factor in reaching higher railway speeds is the recent federal law requiring all trains to have a positive train control safety system, where automated devices manage train separation to avoid collisions, as well as to prevent excessive speeds and deal with track repairs and other temporary situations. What are called high-speed trains in the United States, averaging 70 miles per hour, need gate controls at grade crossings, upgraded tracks, and trains with tilt technology – as on the Acela trains – to permit faster speeds around curves. The Virgin Trains in Florida have diesel-electric locomotives with an electrical generator on board that drives the train but is powered by a diesel engine. 

The faster the train needs to operate, the larger, and heavier, these diesel-electric locomotives have to be, setting an effective speed limit on this technology. The faster speeds possible on the portion of Amtrak’s Acela service north of New Haven, Connecticut, came after the entire line was electrified, as engines that get their power from lines along the track can be smaller and much lighter, and thus go faster. Catenary or third-rail electric trains, like Amtrak’s Acela, can attain speeds of 150 miles per hour, but only a few portions of the tracks now permit this, and average operating speeds are much lower.

Possible alternatives to fast enough trains

True electric high-speed rail can attain maximum operating speeds of 150 to 220 miles per hour, with average operating speeds from 120 to 200 miles per hour. These trains need their own grade-separated track structure, which means new alignments, which are expensive to build. In some places the property-acquisition problem may make a new alignment impossible, unless tunnels are used. True high speeds may be attained by the proposed Texas Central train from Dallas to Houston, and on some portions of the California High-Speed Rail line, should it ever be completed. All of the California line is to be electrified, but some sections will be conventional tracks so that average operating speeds will be lower.


Maglev technology is sometimes mentioned as the ultimate solution to attaining high-speed rail travel. A maglev train travels just above a guideway using magnetic levitation and is propelled by electromagnetic energy. There is an operating maglev train connecting the center of Shanghai to its Pudong International Airport. It can reach a top speed of 267 miles per hour, although its average speed is much lower, as the distance is short and most of the trip is spent getting up to speed or decelerating. The Chinese government has not, so far, used this technology in any other application while building a national system of long-distance, high-speed electric trains. However, there has been a recent announcement of a proposed Chinese maglev train that can attain speeds of 375 miles per hour.

The Hyperloop is a proposed technology that would, in theory, permit passenger trains to travel through large tubes from which all air has been evacuated, and would be even faster than today’s highest-speed trains. Elon Musk has formed a company to develop this virtually frictionless mode of travel, which would have speeds to make it competitive with medium- and even long-distance airplane travel. However, the Hyperloop technology is not yet ready to be applied to real travel situations, and the infrastructure to support it, whether an elevated system or a tunnel, will have all the problems of building conventional high-speed rail on separate guideways, and will also be even more expensive, as a tube has to be constructed as well as the train.

Megaregions need fast enough trains now

Even if new technology someday creates long-distance passenger trains with travel times competitive with airplanes, passenger traffic will still benefit from upgrading rail service to fast-enough trains for many of the trips within a megaregion, now and in the future. States already have the responsibility of financing passenger trains in megaregion rail corridors. Section 209 of the federal Passenger Rail Investment and Improvement Act of 2008 requires states to pay 85 percent of operating costs for all Amtrak routes of less than 750 miles (the legislation exempts the Northeast Corridor) as well as capital maintenance costs of the Amtrak equipment they use, plus support costs for such programs as safety and marketing. 

California’s Caltrans and Capitol Corridor Joint Powers Authority, Connecticut, Indiana, Illinois, Maine’s Northern New England Passenger Rail Authority, Massachusetts, Michigan, Missouri, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Texas, Vermont, Virginia, Washington, and Wisconsin all have agreements with Amtrak to operate their state corridor services. Amtrak has agreements with the freight railroads that own the tracks, and by law, its operations have priority over freight trains.

At present it appears that upgrading these corridor services to fast-enough trains will also be primarily the responsibility of the states, although they may be able to receive federal grants and loans. The track improvements being financed by the State of Michigan are an example of the way a state can take control over rail service. These tracks will eventually be part of 110-mile-per-hour service between Chicago and Detroit, with commitments from not just Michigan but also Illinois and Indiana. Fast-enough service between Chicago and Detroit could become a major organizer in an evolving megaregion, with stops at key cities along the way, including Kalamazoo, Battle Creek, and Ann Arbor. 

Cooperation among states for faster train service requires formal agreements, in this case, the Midwest Interstate Passenger Rail Compact. The participants are Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin. There is also an advocacy organization to support the objectives of the compact, the Midwest Interstate Passenger Rail Commission.

States could, in future, reach operating agreements with a private company such as Virgin Trains USA, but the private company would have to negotiate its own agreement with the freight railroads, and also negotiate its own dispatching priorities. Virgin Trains says in its prospectus that it can finance track improvements itself. If the Virgin Trains service in Florida proves to be profitable, it could lead to other private investments in fast-enough trains.

Jonathan Barnett is an emeritus Professor of Practice in City and Regional Planning, and former director of the Urban Design Program, at the University of Pennsylvania. 

This is an extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, published now by Island Press. You can find out more here.