A buttress is a structure built against a wall, slope, or other surface to brace and strengthen it against lateral forces. The concept is simple: when something tall or heavy risks being pushed sideways or collapsing outward, a buttress transfers that force safely downward into the ground. While most people encounter the term in architecture, the buttress principle shows up in fields ranging from dam engineering to tropical ecology to human bone surgery.
Buttresses in Architecture
The most familiar buttress is the stone or brick projection built against the exterior wall of a building. A standard buttress is essentially a thick column of masonry bonded to a wall, adding mass and rigidity at the point where outward forces are greatest. You can see simple buttresses on medieval churches, barns, and fortress walls, where they appear as evenly spaced rectangular supports along the outside.
The flying buttress took this idea further during the Gothic era. Instead of a solid mass pressed against the wall, a flying buttress uses an arched arm that reaches from a freestanding pier to the upper portion of the wall, transmitting the outward thrust of the roof or vault down and away from the building. This design increased the supporting power of the buttress while freeing up the wall itself. Because the wall no longer had to bear all the lateral load, builders could make it thinner and fill it with the enormous stained-glass windows that define Gothic cathedrals. Flying buttresses are the reason churches like Notre-Dame de Paris could have soaring ceilings and walls that seem to be made more of glass than stone.
The buttress concept didn’t stop in the medieval period. The structural system behind the Burj Khalifa, the world’s tallest building, is called a “buttressed core.” Engineer William F. Baker designed a Y-shaped floor plan in which three wings brace each other through a six-sided central core. When wind pushes against one side, the opposite arm naturally resists the force, much like an I-beam resisting bending. Each wing effectively buttresses the others, allowing the tower to reach over 800 meters without excessive material use. Baker has said this system ushered in a new era of supertall building design.
Buttress Dams
In civil engineering, a buttress dam uses a series of vertical or sloping supports on its downstream face to hold back a reservoir. A standard gravity dam resists water pressure through sheer mass: it’s a massive wall of concrete heavy enough that the water can’t push it over. A buttress dam achieves the same goal with far less material by channeling forces through its buttresses directly into the foundation below.
Sometimes called multiple arch dams or Ambursen dams (after engineer Nils F. Ambursen, who patented the approach in the early 1900s), these structures use a relatively thin upstream face supported by regularly spaced buttresses. The result is a dam that uses 30 to 60 percent less concrete than a gravity dam of comparable size, though it requires more complex engineering and formwork to build. Buttress dams are typically made of concrete or masonry and are best suited for wide valleys with strong bedrock foundations that can accept the concentrated loads from each buttress.
Buttress Roots in Tropical Trees
Walk through a tropical rainforest and you’ll notice that many large trees have wide, flat, fin-like roots flaring out from the base of the trunk. These are buttress roots, and they serve the same purpose as architectural buttresses: bracing something tall against sideways forces.
Tropical rainforest soil is often shallow and nutrient-poor, which means tree roots spread outward rather than growing deep. Trees in these environments evolved buttress roots because competition for sunlight drove them to grow tall quickly, and that rapid vertical growth required extra structural support near the base. The broad, plate-like roots increase the tree’s stability against wind and its own weight without needing a deep taproot system.
Beyond mechanical support, buttress roots serve ecological roles. They create what researchers call “root walls” that slow the downhill flow of soil and organic material on slopes, reducing erosion. One hypothesis suggests they also help trees absorb nutrients and water more efficiently from nutrient-depleted soils by increasing the surface area in contact with the topsoil layer. Common buttress-rooted species include trees in the genera Castanopsis, Pterospermum, and many others found across Southeast Asian and South American tropical forests.
Buttresses in the Human Skeleton
Your facial skeleton is organized around a system of horizontal and vertical buttresses: reinforced ridges of bone that absorb and distribute the forces of chewing, impact, and gravity. These bony pillars connect the teeth and jaw to the upper skull, channeling mechanical stress along predictable pathways. When surgeons repair complex facial fractures, they prioritize restoring these buttress lines with metal plates to rebuild the structural framework that holds the midface together.
In orthopedic surgery more broadly, a “buttress plate” is a metal plate applied to a fractured bone to prevent fragments from shifting under load. These plates are commonly used near joints, where a piece of bone has been sheared or split by force. The plate is positioned so it forms a supportive angle with the intact bone, blocking the broken fragment from sliding out of alignment as weight or muscle force is applied. Think of it as a bookend holding a fragment in place while it heals.
Buttresses in Geology and Slope Engineering
Geologists and civil engineers use the term “buttress” for both natural rock formations and engineered slope stabilization. A natural rock buttress is a protruding ridge or mass of competent rock that braces an adjacent slope or cliff face, preventing movement of weaker material behind it.
In slope engineering, a buttress fill is one of the most common techniques for stabilizing unstable ground. The process involves removing the outer face of a weak or poorly consolidated slope and replacing it with engineered, compacted fill material. This fill is “keyed” into solid underlying rock or soil so it can’t slide, and it typically finishes at a slope gradient of 2:1 (two feet horizontal for every one foot vertical). Buttress fills are effective at stabilizing deep-seated landslides and weak sedimentary formations, though they require large-scale grading and significantly alter the natural contour of the landscape. In southern California, where weak sedimentary rock is common, buttress fills have been used extensively to make hillside development possible.
The Common Principle
Whether it’s a stone pier bracing a cathedral wall, a concrete slab holding back a reservoir, a tree root stabilizing a 40-meter trunk, or a metal plate keeping a fractured bone aligned, every buttress works on the same principle. It redirects forces that would cause sideways failure and channels them into a stronger foundation. The word comes from the Old French “bouterez,” meaning “to thrust,” and that basic mechanical idea, resisting thrust, connects every use of the term across disciplines.