How we learned to build

From a hilltop raised by hunters to the material that must now be redesigned

A The oldest monumental architecture yet found was built by people who had not invented agriculture, pottery or writing, and its existence has forced a revision of the order in which those things were assumed to have happened. At a hilltop site in southern Turkey, hunters raised circles of carved limestone pillars, some weighing many tonnes, around eleven and a half thousand years ago. The conventional sequence had held that farming produced surpluses, surpluses produced towns, and towns produced monuments. Here the monument comes first, and the settled farming villages appear in the same region afterwards, which has led some archaeologists to reverse the causation entirely: the effort of building and feeding the builders may have been among the pressures that produced cultivation.

B The site raises a second difficulty that is rarely acknowledged. Monumental building requires not only labour but organisation — someone to decide what is built, someone to feed the workers, someone to settle disputes — and the pillars therefore imply a social arrangement more elaborate than the term hunter-gatherer usually suggests. Whether that arrangement was permanent or assembled seasonally for the work is unknown and probably unknowable. The first ordinary building material was mud, and it remains the material in which more of the world's population lives than any other. Mixed with straw, shaped into bricks and dried in the sun, it is cheap, requires no fuel, insulates well against heat and is durable enough to last centuries if kept dry. Its weakness is that single quality: mudbrick fails when saturated, which is why the technique dominates in dry climates and disappears in wet ones, and why the earliest surviving towns are found where rain is scarce. The apparent geography of early urban life is therefore partly an artefact of preservation: settlements of similar age in wetter regions have simply dissolved, and what survives to be excavated is not a fair sample of what existed.

C Stone solved the durability problem and introduced a geometric one. A stone lintel spanning two uprights can only be so long before it breaks under its own weight, so a building made this way is a forest of closely spaced columns, and its interior is mostly supports. Egyptian temples and Greek ones are magnificent and, considered as enclosures, inefficient: the amount of usable space per tonne of quarried stone is very low. Every subsequent advance in building can be understood as an attempt to enclose more volume with less material.

D The arch was the first real answer, and the Romans exploited it more thoroughly than anyone before them. An arch converts the downward load into a thrust passing along a curve into the ground, allowing a span several times what a lintel permits; extended, it becomes a vault, and rotated, a dome. Combined with a concrete made from lime and volcanic ash, which sets under water and grows stronger over time, it produced enclosed spaces that were not matched for over a thousand years. The largest unreinforced concrete dome ever built dates from this period and still stands, which is a fair measure of how completely the technique was lost afterwards: for a millennium and a half, nobody could build anything comparable, and for much of that time nobody understood how it had been done. Analysis of that concrete has recently shown that lumps of unmixed lime within it dissolve when cracks admit water and recrystallise across the crack, so that the material repairs itself — a property modern concrete does not have and is now being engineered to imitate.

E Both the recipe and the confidence were lost. Medieval builders in northern Europe worked in stone without concrete and pursued height rather than span, discovering that the outward thrust of a tall vault could be caught by external props transferring it to the ground beyond the walls. This freed the wall itself from its structural duty, which is why the great churches of the period could replace masonry with glass over most of their surface. It was an elegant solution reached by trial, error and occasional collapse, since the mathematics that would have predicted the forces did not yet exist.

F The nineteenth century changed the material and therefore the possibilities. Iron and then steel provided a frame far stronger in tension than any masonry, so that a building could be a skeleton with a skin rather than a stack of load-bearing walls; the accompanying invention of the safety lift made the resulting height usable. Reinforced concrete combined the two ideas, embedding steel bars where the concrete would otherwise be pulled apart, and produced a material that could be poured into any shape and that now accounts for the overwhelming majority of construction worldwide. The combination works because the two materials happen to expand and contract at nearly the same rate when heated, a coincidence without which the composite would tear itself apart in the first hot summer.

G That ubiquity is the current problem. Manufacturing cement releases carbon dioxide twice over — from the fuel used to heat the kiln, and from the limestone itself, which gives off the gas as it is converted — and the industry accounts for something in the region of seven or eight per cent of global emissions. Alternatives exist at various stages of development: cements using different chemistry, mixes incorporating industrial waste, and a renewed interest in timber for tall buildings. None is yet available at the scale required. The material that let humanity build the modern world has become the thing that must be redesigned before very much more of it is built.