Raw earth has produced two of the most radically different answers ever given to the same construction problem: how to live in dense communities in arid climates, without enough stone or timber. Shibam, in Yemen, answered by building upward. The villages of the Sahel answered by building a system of collective maintenance capable of keeping the planet's most fragile architecture alive for centuries. Neither solution is "more primitive" than the other: they are two different social engineerings applied to the same humble material.
Four ways of building with earth
Before looking at the cities, it helps to distinguish the techniques, because "earth building" covers very different construction families. Adobe, or mud brick, is a block of earth mixed with water and often straw, shaped in a wooden mould and left to dry in the sun: it is the technique of Shibam, Djenné and much of the Middle East and Latin America. Rammed earth, or pisé, is made by compacting layers of damp earth inside wooden formwork, rather as concrete is poured, to form monolithic walls; it is found from Morocco to China, and in Europe from France to Piedmont. Cob is a mix richer in straw, shaped directly by hand, layer upon layer, without moulds or formwork. Wattle and daub, finally, is a framework of timber or reeds coated with a mix of earth and fibres, a light technique used all over the world.
Each technique behaves differently. Adobe allows fast building with unskilled labour and lets the blocks dry before laying, reducing wall shrinkage; rammed earth gives denser, stronger walls but requires formwork and a great deal of compaction work; cob adapts to free and curved forms; wattle and daub is light and performs better in earthquakes. In all of them, however, quality depends on the soil: the right proportion is needed between clay, which acts as the binder, and sand and gravel, which give structure. Too much clay makes the wall crack as it dries, too little makes it crumbly. That is why local building traditions are above all a knowledge of the local soil, accumulated over centuries of trial and error.
Shibam: the mud skyscraper before the skyscraper
The old city of Shibam, in Yemen's Wadi Hadhramaut valley, is nicknamed "the Manhattan of the desert" — a phrase coined by the writer and explorer Freya Stark in the 1930s that has remained, ever since, the most effective way to describe the city's visual effect to anyone who hasn't seen it in person. Around five hundred tower buildings, five to eleven storeys tall and in some cases over thirty metres high, are packed onto a compact area ringed by defensive walls. Most of today's towers date from the rebuilding that followed a devastating flood in 1532, even though the settlement itself has almost two thousand years of history.
The building logic wasn't aesthetic but strategic on two fronts: building vertically saved the valley's scarce farmland, cultivated at the foot of the towers, and offered protection from the Bedouin raids of the time. Each floor typically houses one or two rooms, with wall thickness progressively reducing with height — thicker and load-bearing at the base, thinner on the upper floors — a principle of structural optimisation similar to the one that, centuries later, would govern the tapering of steel and reinforced-concrete skyscrapers. UNESCO recognised Shibam as a World Heritage Site in 1982, calling it "the best example of urban planning based on the principle of vertical construction" applied to a material that, elsewhere, is associated almost exclusively with low structures.
Looking closely at the towers shows how Shibam's builders dealt with the material's weak points. The houses rest on stone bases that separate them from ground moisture and from the wadi's floods. Floors and lintels are of timber, often palm or acacia, and the projecting beams also make the division into storeys legible from outside. The upper parts of the towers and their crowns are often rendered with white lime, more resistant than earth to rain erosion, and the flat roofs are periodically refreshed with new layers of earth. At Shibam too, then, durability depends on maintenance: an abandoned tower begins to decay from the top, where the rain strikes first, and within a few years can become unsafe.
Precisely for this reason the city is fragile today. In 2008 a tropical storm and the floods that followed damaged the foundations of many houses; since 2015, with the war in Yemen, Shibam has been on the List of World Heritage in Danger, and the lack of resources and maintenance has led in recent years to the collapse of several buildings after heavy rain. It is the most dramatic demonstration of the principle running through this whole article: earth architecture is not fragile in itself, but becomes fragile when the social work that keeps it alive is interrupted.
The Sahel: maintenance as construction technology
If Shibam solves the density problem with height, the building tradition of the African Sahel — from the Great Mosque of Djenné, in Mali, to the region's hundreds of smaller villages — solves a different problem, durability in a climate of intense seasonal rains, with a strategy that isn't technical but social: periodic collective maintenance. The Great Mosque of Djenné, the largest unfired-brick structure in the world, with a 75×75-metre plan and 16-metre minarets, is replastered every year by the whole community in a collective ceremony involving hundreds of people. It isn't a cultural event incidental to construction — it is the construction technology itself, applied as a continuous process rather than a one-off intervention.
This strategy radically shifts the criterion for judging the "durability" of a raw-earth building: a wall in Djenné isn't designed to last decades without intervention, the way a stone or concrete wall would be — it's designed to be renewed every season, in a cycle that, as long as the social community sustaining it remains intact, can in principle continue indefinitely. It's a durability model that depends on social continuity as much as on construction technique — an aspect often overlooked when raw earth is judged only by the parameters of materials engineering.
The Great Mosque we see today was rebuilt in 1907 on the ruins of an earlier building, under the leadership of the head of the Djenné masons' guild, the barey ton, a brotherhood that handed down techniques and trade secrets from generation to generation. The façades are pierced by hundreds of palm-wood poles, the toron, projecting from the wall: they are at once decoration, reinforcement and permanent scaffolding, because it is by climbing them that the men reach the upper parts during maintenance. The plaster, called banco, is a mix of clayey earth and water left to ferment for days with rice husks or other plant fibres, which make it more workable and less prone to cracking.
The crépissage festival, the renewal of the plaster, is held every year before the rainy season. In the preceding days the banco is prepared in pits along the river; then, in a single day, the men of the town's various districts climb the walls and apply the new coat by hand, while women and boys carry water and mix, amid music and a friendly competition between districts to finish first. The guild masons direct the work and check the quality. An architect would be hard pressed to find a clearer example of how a building can be at once a constructed object and a social institution.
Other earthen cities
Shibam and Djenné are the most famous cases, but the geography of earth building is much wider. In Peru, Chan Chan, capital of the Chimú kingdom that flourished before the Incas, is the largest earthen city of pre-Columbian America, with adobe enclosure walls decorated in relief. In New Mexico, Taos Pueblo has been continuously inhabited for about a thousand years, in multi-level adobe buildings that are renewed with fresh earth plasters. In China's Fujian province the tulou, large circular or square rammed-earth buildings that housed entire family clans around a courtyard, became a UNESCO World Heritage Site in 2008. In Morocco, ksour such as Aït Benhaddou show fortified villages of rammed earth and mud brick along the old caravan routes.
There is also a case that shows the material's main limitation. The citadel of Bam, in Iran, was one of the largest earthen complexes in the world, with walls, towers and an entire historic town built of adobe. The earthquake of 26 December 2003 destroyed it almost completely and killed tens of thousands of people in the surrounding modern town, where many dwellings were also of unreinforced earth. Traditional earth construction has very low resistance to the tensile stresses caused by tremors, and in seismic zones it must be designed with reinforcement, ties and suitable forms: this is the subject of the in-depth piece on seismic behaviour.
One material, endless local answers
The thread linking these two traditions, together with the already familiar ones from the Andean, Mesopotamian and North African worlds, is that none of them treats raw earth as a compromise accepted for lack of better alternatives. Each has developed, over time, a technical and social response specific to its own climatic and economic context — verticality in Shibam to make the most of scarce land and to defend itself, ritual maintenance in the Sahel to cope with a climate of destructive seasonal rains, thick walls and formwork-free vaults in Hassan Fathy's Egypt for natural ventilation. Understanding this variety of solutions is useful not out of nostalgia, but because contemporary research on raw earth — seismic codes, modern stabilisation, the work of Kéré and Heringer — builds explicitly on this repertoire of local solutions, rather than replacing it.
And in Italy?
Italy too has an earth-building tradition, less well known than that of the great international sites but still visible. In Sardinia, especially in the Campidano, courtyard houses are built with ladiri, sun-dried bricks of earth and straw. In Abruzzo and the Marche there are houses in massone, built by hand-shaping large loaves of earth mixed with straw, a technique similar to cob; at Casalincontrada, in the province of Chieti, a museum and an association look after their conservation. In the plain around Alessandria, in Piedmont, the Frascheta area preserves many rural buildings in rammed earth. They are humble buildings, often abandoned or altered, but they document a building know-how that was normal in Italy too until the mid-20th century.
All these traditions share a physical logic that still holds today. In a climate with large differences between day and night, a thick earth wall stores heat during the day and releases it slowly in the cool hours, with a lag of several hours: the interior stays more stable than the outside without any mechanical plant. Earth also absorbs and releases moisture from the air, damping peaks in indoor humidity. And they all share the same practical rule, summed up by a saying found in many languages: an earth house needs good boots and a good hat, that is, a plinth separating it from ground moisture and a roof protecting it from rain. Between the boots and the hat, the wall can last for centuries.