Oxford Mathematician Debunks Parthenon Optical Illusion Fix Myth

Scholars have long admired the temple on the Acropolis hill, praising its architects for using geometry to refine its appearance. Its subtle curves were said to compensate for optical effects that would otherwise make the building’s clean lines look distorted.

Goriely traces the idea to the 1st-century Roman architect and engineer Vitruvius, who wrote about the Parthenon about 400 years after it was built. Vitruvius’s account entered architectural books and became established fact. The mathematician said modern AI chatbots still repeat the story. “I do think it might be the oldest myth that we have,” Goriely said, “apart from religion.”

One common claim concerns the Parthenon’s base, or stylobate. Measurements show its sides are not horizontal but form a gentle arc that rises 6cm in the centre. According to Vitruvius, this corrects an illusion that would make the base appear to sag in the middle.

The sagging effect has been attributed to two proposed tricks of light. The first holds that long horizontal lines seem to slump in the middle, but Goriely found no evidence for this. The second suggests the Parthenon’s marble columns create the illusion, based on the Hering illusion, in which parallel lines on a two-dimensional surface can look bowed when other lines intersect them. Goriely said the Hering illusion is strongest when intersecting lines are at acute angles; the Parthenon’s columns are too vertical to produce it, and there is no proof the effect works in three dimensions.

Another claim is that bulges in the columns, a curvature called entasis, correct an optical illusion that would make them look too narrow in the middle. Goriely found no evidence for that illusion either. He added that the columns bulge by only 18mm, which is barely perceptible at typical viewing distances.

Goriely assesses and dismisses other supposed optical corrections in the paper, and concedes that he “fell into a bit of a rabbit hole” pulling the evidence together. He suspects the Parthenon’s architects had other reasons for the features. The curve of the base may have prevented rain puddles from forming, while curved columns might simply have felt more organic and visually pleasing to the ancient Greeks, he writes.

It is unclear why the myth has endured, but Goriely suspects that the perception of ancient Greece as a supremely knowledgeable and ingenious civilisation is partly to blame. Unusually for an academic study, he ends his paper by inviting readers to put it down and take a walk in a city. “Trust your own eyes, question what you see and decide for yourself whether the theory of optical corrections holds up,” he writes.

Frank Salmon, professor of the history of classical architecture at the University of Cambridge, said some experts had long been cautious of Vitruvius’s explanations. “Some experts have long been cautious of Vitruvius’s explanations, recognising the risks inherent in using his text as a sort of bible to explain architectural practices in Greece centuries before his time, but also the loss of the many Greek texts about their temple architecture he claimed to have read when preparing his own,” Salmon said.