The Parthenon’s architectural illusions are a myth

Ancient Greek architects are said to have designed the Parthenon with curved lines to make it appear perfectly straight – but these claimed optical illusions are a myth, according to a mathematician.

The giant temple, built in the 5th century BC in Athens, is considered to be the culmination of the Doric style of classical Greek architecture. It is 69.5 metres long and 30.9 metres wide and, although appearing straight, famously has almost no straight lines or right angles.

The enduring hypothesis is that it was built with architectural refinements to counteract the visual illusions that a viewer would experience. Essentially, they thought straight lines would look curved, so they built it curved to make it look straight.

Advertisement

“It’s widely accepted that it was made this way on purpose,” says Alain Goriely at the University of Oxford. “But there is strictly no evidence that the refinements in the Parthenon actually produce the proposed visual illusions.”

Goriely has examined 12 proposed optical corrections and found that they are either unsupported by evidence or too small to have a perceptible effect under typical viewing conditions.

Free newsletter

Sign up to The Daily

The biggest illusion claim is that the upward curve in the middle of many horizontal elements – also seen in other temples – is there so it doesn’t look as if the elements sag. This includes the stepped base on which the columns stand – known as the stylobate – as well as the horizontal entablature across the tops of the columns.

Goriely calculates that viewers wouldn’t perceive any sagging, so this illusion doesn’t stand up. “There are certain effects such as the Hering illusion that, on paper, would give qualitatively the same direction of effect, but if you actually do the computation, you realise that the effect does not appear. And although it might work on paper, the effect in the real 3D building with an observer is completely different.”

A more likely reason for the curve – put forward before but dismissed in the 1800s – would be that the small gradients help water to drain away and prevent the formation of puddles, although we can’t know definitively what the thinking was behind the construction, says Goriely.

Marge Livingstone, a neuroscientist who studies visual perception at Harvard Medical School, doesn’t think the floor was curved to create an illusion. “I think it must have been for drainage, just like on roads,” she says. 

John Senseney at the University of Arizona in Tucson says the curvature throughout the building is a consequence of the curve of the platform on which it was built.

“The refinement of convex curvature is an extraordinarily sophisticated product of the expert knowledge, judgement, tools and techniques of common and, often, enslaved labourers working collaboratively on site,” he says. “It is not a product of an elite architect’s mathematical prowess created abstractly and then executed by the builders. And this curvature is not a product of an intended optical correction.”

Among the other proposed illusions are that the columns have a slight bulge in their middles to prevent them from appearing pinched, and the corner columns were thicker than the internal ones to offset the stronger light around the edges that would make them seem thinner.

Goriely thinks no such pinching illusion has ever been scientifically demonstrated, even in controlled tests using three-dimensional reconstructions of temples. He says simpler explanations could be that the builders used curved columns because they believed them to look more pleasing than straight ones, or that shaping them that way improves the resistance against buckling. The corner columns could also be bigger because they carry a slightly heavier load, he says.

“If the columns do get narrower at the top, that could be to make them seem taller, or just because, for stability, one wants a base thicker than the top,” says Livingstone.

Ancient Greeks were aware of the existence of visual illusions, but there is no evidence they made the Parthenon to counteract the ones often cited, and the myths have never been universally accepted among experts, says Goriely.

The first mentions of the Parthenon being designed with optical illusions in mind come from Vitruvius’s De architectura (On architecture), written some 400 years after the temple was built, he says.

The ideas have since taken hold so strongly because they capture the imagination, much like the now disproven idea that the Parthenon was built to fit the golden ratio, says Goriely. “Myths that are so powerful are very hard to change. Look at religion, right?”

Royal Society Open Science DOI: 10.1098/rsos.260999