What is an abacus in architecture?
An abacus is the square or rectangular slab that sits on top of the capital of a column. It forms the transition between the capital (the decorative upper section of the column) and the entablature (architrave) that rests on it. The abacus is an essential structural and decorative element of the classical orders of architecture.
Function
The abacus has a clear structural role: it distributes the load from the entablature evenly across the capital and the column shaft. Without the abacus, the pressure would be concentrated on too small an area, which could damage the capital.
The shape and finish of the abacus varies by order:
- Doric — simple, unadorned square slab
- Ionic — narrower and often lightly moulded
- Corinthian — the sides are concave (inwardly curved) and the corners bevelled, sometimes decorated with a rosette
- Tuscan — plain and austere, similar to the Doric version
- Composite — a combination of Ionic and Corinthian features
Application
The abacus originates from Greek and Roman architecture, but has been used throughout the centuries in virtually every architectural period that drew on classical forms:
- Classical temples — every column has an abacus as part of the capital
- Renaissance and Neoclassicism — reintroduction of the classical orders with carefully detailed abaci
- Contemporary architecture — sometimes used as a decorative element or reference to the classical tradition
Related terms
- Capital
- Column
- Classical orders
- Architrave
- Entablature
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