A buttress is an architectural structure built against or projecting from a wall which serves to support or reinforce the wall. Buttresses are fairly common on more ancient buildings, as a means of providing support to act against the lateral (sideways) forces arising out of the roof structures that lack adequate bracing.

Vicolo di Formia (1956)
Oil painting by Antonio Sicurezza of an alleyway with flying buttresses between buildings

Vicolo di Formia (1956) Oil painting by Antonio Sicurezza of an alleyway with flying buttresses between buildings

The term counterfort can be synonymous with buttress and is often used when referring to dams, retaining walls and other structures holding back earth.

Early examples of buttresses are found on the Eanna Temple (ancient Uruk), dating to as early as the 4th millennium BC.[citation needed]

In addition to flying and ordinary buttresses, brick and masonry buttresses that support wall corners can be classified according to their ground plan. A clasping or clamped buttress has an L shaped ground plan surrounding the corner, an angled buttress has two buttresses meeting at the corner, a setback buttress is similar to an angled buttress but the buttresses are set back from the corner, and a diagonal (or 'French') buttress is at 135° to the walls (45° off of where a regular buttress would be).

The gallery below shows top-down views of various types of buttress (dark grey) supporting the corner wall of a structure (light grey).

Angled buttress

Clasping or clamped buttress

Diagonal or 'french' buttress

Setback buttress

A buttress and a flying buttress, mostly concealed, supporting walls at the Palace of Westminster

Buttress at Our Saviour's Chapel, Żejtun, Malta

Façade buttresses at Milan Cathedral, Italy

Buttresses on the 700ft tall Daniel-Johnson Dam, Quebec

Thick buttresses characterize Earthquake Baroque architecture like Paoay Church, Philippines

Buttresses of the western side of the Mosque of Uqba in Kairouan, Tunisia

Buttresses to support the wall of this row house were constructed after its neighboring house was taken down as part of the Centralia mine fire.

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