Brick, stone and the arch: how early builders made weak-in-tension materials span and soar

For most of human history, the great buildings of the world were made of materials that are strong when squeezed but weak when pulled: mud brick, fired brick, stone and early concrete. Masonry can carry enormous loads in compression but cracks easily in tension. A stone beam spanning between two columns breaks at quite modest spans, because its underside is stretched. Yet with these materials, builders created ziggurats, temples, aqueducts, domes and cathedrals, some of which still stand after two thousand years.

They did it through geometry. By shaping buildings so that the forces within them flowed through the material in compression, builders made weak-in-tension materials span great distances and rise to remarkable heights. They learned how to do this mostly by experience, rules of proportion and occasionally by failure, centuries before anyone could calculate stresses. The story of masonry construction is therefore a story about matching form to material, about the power and limits of accumulated experience and about construction methods that shape what can be built.

This article traces, in general terms, how masonry construction developed from early brick and stone buildings through the arch, Roman engineering and concrete, to Gothic vaulting, and on to masonry in modern Australia, and draws out lessons for designers, builders and business leaders. It is a general historical overview, not engineering advice.

Mud, fire and bitumen

Some of the earliest cities, in Mesopotamia, were built largely of sun-dried mud brick, made from abundant clay and straw. Mud brick is cheap and easy to make but vulnerable to water. Builders protected it with fired brick, baked in kilns to make it harder and more durable, often laid with bitumen mortar in exposed or wet locations. Monumental ziggurats, stepped temple platforms, combined a mud-brick core with a facing of fired brick. These structures relied on sheer mass: thick walls and stepped forms that kept loads in compression and spread them over large areas.

Post and lintel

Egyptian and Greek builders developed the post-and-lintel system: vertical columns supporting horizontal stone beams. It produced some of the most admired buildings in history, but it had a fundamental limit. A stone lintel bends under its own weight and the load above, putting its lower face in tension. Because stone is weak in tension, lintels had to be deep and spans short, which is why classical temples have closely spaced columns. Interiors were crowded with supports.

Corbelling

One way to bridge wider openings with stone was corbelling: each course of stone projects slightly beyond the one below, stepping inward until the two sides meet. Corbelled vaults and domes appear in many ancient cultures, including the beehive tombs of Bronze Age Greece. Corbelling works because each stone is held down by the weight above it, but it requires thick walls and limits the shape of the space.

The true arch

The true arch changed what masonry could do. An arch is made of wedge-shaped blocks, called voussoirs, arranged in a curve with a keystone at the top. Under load, the voussoirs press against each other, so the whole arch carries load in compression, transferring it down and outward to its supports.

Two features of arches shaped building practice for millennia:

• Thrust. An arch pushes outward at its base. The supports, or abutments, must resist that thrust, or the arch spreads and collapses. Buttresses, thick walls and adjacent arches were used to contain it.
• Centring. An arch cannot stand until the keystone is in place. During construction, it must be supported on temporary timber framework called centring, which is removed once the arch is complete. The construction method was as important as the final design.

Later scientific understanding explained why good arches work: the line along which forces flow through the arch, the line of thrust, must stay within the masonry. In the seventeenth century, Robert Hooke observed that the ideal shape for an arch is that of a hanging chain turned upside down, because the chain hangs in pure tension and the inverted shape carries load in pure compression.

Roman engineering

The Romans used the arch with extraordinary range and confidence. Arches carried roads over rivers and aqueducts across valleys, such as the Pont du Gard in southern France, which carried water across the Gardon river in the first century AD. Arches formed the facades of amphitheatres and the structure of vaults and domes.

Roman concrete

The Romans also developed concrete on a large scale. Their concrete combined lime with volcanic ash, known as pozzolana, and aggregates. The volcanic ash reacted with lime to produce a strong, durable material that could set even underwater, which made it ideal for harbours and foundations. Concrete could be cast into shapes that would be difficult in cut stone, using formwork, and it freed builders from relying entirely on skilled stonecutting.

The Pantheon

The Pantheon in Rome, completed in the second century AD, is a striking demonstration. Its concrete dome, about 43 metres across, remains the largest unreinforced concrete dome in the world. Its builders reduced the weight towards the top by using lighter aggregates in the upper parts of the dome and by forming coffers, recessed panels, in its underside. An open oculus at the crown removes the part of the dome that would otherwise be most problematic and admits light. The dome works because it acts in compression, with its thrust contained by massive supporting walls.

Domes after Rome

Two later domes show how builders kept extending what masonry could do, and how construction method shaped the result.

Hagia Sophia in Constantinople, completed in 537, placed a great dome over a square plan. The transition from the square base to the circular dome was made with pendentives, curved triangular sections of masonry that carry the dome’s weight down to four massive piers. The arrangement opened a vast interior, but it pushed the structure hard. After earthquakes, the original dome partially collapsed in 558 and was rebuilt with a taller profile, which reduced its outward thrust. The building has needed repair and strengthening many times since, a reminder that ambitious structures carry ongoing obligations.

The dome of Florence Cathedral, built between 1420 and 1436 to a design by Filippo Brunelleschi, faced a different problem. The octagonal opening was so wide that building conventional timber centring across it was considered impractical. Brunelleschi’s solution used two shells, an inner and an outer dome tied together, and laid the brickwork in a herringbone pattern that helped each new course hold itself in place while the mortar set. He also designed hoisting machines to lift materials to the working level. The dome was built without full centring, a case where solving the construction problem was the design.

Gothic vaults

Medieval builders in Europe developed another way to make masonry soar. Gothic architecture, emerging in France in the twelfth century, combined three structural ideas:

• The pointed arch, which directs thrust more steeply downward than a semicircular arch and allows arches of different spans to reach the same height, giving designers more freedom.
• The ribbed vault, in which stone ribs form a framework that carries the vault’s weight to specific points, with lighter infill panels between them.
• The flying buttress, an external arch that carries the outward thrust of the high vaults across the side aisles to buttress piers.

Together these concentrated loads into a skeleton of piers, ribs and buttresses, allowing walls between them to be thin and filled with large windows of stained glass. Gothic cathedrals reached remarkable heights and opened their interiors to light.

Rules of proportion and their limits

Gothic master masons had no theory of stresses. They designed using geometric rules of proportion, passed down through training and experience, that related the thickness of piers and buttresses to spans and heights. Those rules worked well within the range of experience. When builders pushed beyond it, failures could follow. The choir vaults of Beauvais Cathedral in France, among the tallest ever attempted, partially collapsed in 1284 and had to be rebuilt with additional supports. Such failures were part of how the tradition learned.

Masonry in modern Australia

Brick and stone remain central to Australian building. Sandstone public buildings, brick terraces, warehouses and homes shape the character of many cities. Modern masonry is designed using engineering standards, including the Australian standard for masonry structures, and often incorporates reinforcement, ties and other measures to resist tension, wind and earthquakes. Brick veneer construction, in which a brick outer skin is tied to a timber or steel frame that carries the structural loads, became a common form of Australian housing.

Unreinforced masonry, typical of older buildings, performs poorly in earthquakes because it cannot resist the tension and shear forces that shaking produces. The 1989 Newcastle earthquake caused deaths and extensive damage, much of it to older unreinforced masonry buildings, and highlighted the importance of assessing and strengthening such structures. Heritage masonry buildings also need appropriate materials and methods for repair; using modern hard cement mortars on soft historic brick, for example, can damage the brick over time. The building regulation for project teams article explains how the National Construction Code and standards apply to building work.

Lessons for designers and businesses

Shape the design to the material

Masonry succeeded when builders shaped structures to keep it in compression. Every material has strengths and weaknesses, and good design works with them rather than against them. The same applies to plastics, composites, timber and steel, and, by analogy, to organisations and people: arrangements that use strengths and avoid weaknesses perform better.

Geometry can matter more than strength

A well-shaped arch of modest stone can outperform a massive beam of the same material. Often the arrangement of parts, not the strength of each one, determines how a system performs.

Construction method shapes what can be built

Centring, formwork and scaffolding made arches, vaults and domes possible. In modern projects, how something will be built, transported and installed is as important as the finished design. The building up and boring down article explores how construction methods shaped later buildings and tunnels.

Experience works within its range

Rules of proportion served builders well until they were extrapolated beyond experience. Rules of thumb, templates and past practice are valuable, but they can fail when applied to larger, faster or different situations. That is where analysis, testing and caution matter most.

Failures teach

Collapses such as Beauvais taught builders the limits of their methods. The what engineering failures teach any business article shows how modern investigations turn failures into lasting lessons.

Durability is designed in

Roman concrete and well-built masonry have lasted for centuries. Designing for durability, with suitable materials, protection from water and maintainable details, creates value that outlasts its builders.

A worked example

This is an illustrative example. The building and events are hypothetical.

A small manufacturer buys an old brick warehouse with load-bearing brick walls and plans to cut a large new opening in one wall for a roller door, to improve truck access. The builder’s first plan is simply to cut the opening and install a steel lintel above it.

An engineer engaged for the project points out several issues. The wall is unreinforced masonry carrying the roof trusses, and the new opening removes a section that currently carries load in compression down to the foundation. The masonry above the opening must be supported during work by temporary props and needles, a modern equivalent of centring. The new lintel and the piers either side of the opening must carry the redirected loads, and the piers may need strengthening. The engineer also notes cracking near an existing opening and recommends investigating the foundations before work starts. Because the building is old, the engineer checks whether heritage controls apply and recommends a lime-based mortar for repairs to match the original soft bricks.

The project costs more than the builder’s first estimate, but the wall is altered safely, the cracking is traced to a blocked stormwater drain that had softened the foundation soil, and the drain is repaired before it caused further movement.

How this applies to a small Australian business

• Engage a qualified engineer before altering load-bearing walls, openings or older masonry buildings.
• Respect the material. Masonry needs to stay in compression and be protected from water.
• Plan temporary works. How a change will be supported during construction matters as much as the final design.
• Check heritage requirements for older buildings.
• Investigate cracks before assuming they are cosmetic.
• Be cautious with rules of thumb outside their usual range.

Questions worth considering

• Where in our designs or operations are we working against the strengths of our materials or people?
• How much of our performance depends on arrangement rather than raw capability?
• Have we planned how changes will be built and supported, not just what they will look like?
• Are we applying past experience outside the range where it was proven?
• What have our own failures taught us, and have we recorded the lessons?

Bringing it together

Early builders used materials weak in tension, mud brick, fired brick, stone and early concrete, to create structures of great span and height by shaping them to carry load in compression. Post-and-lintel systems limited spans; corbelling and then the true arch extended them; Roman arches, aqueducts, concrete and domes showed the range of masonry; and Gothic vaults, pointed arches and flying buttresses opened walls to light. Throughout, geometry, construction method and accumulated experience mattered as much as material strength, and failures marked the limits of experience. Those lessons, working with materials, valuing arrangement, planning construction and respecting the limits of rules of thumb, still apply to designers and businesses today.

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Source: KEVOS editorial notes. Examples in this article are illustrations. This article is a general historical overview and does not constitute engineering advice.