New Research

Centuries Ago, an Architect Characterized the Parthenon’s Curves as a Clever Optical Illusion. Now, a Mathematician Begs to Differ

In the first century B.C.E., Vitruvius wrote that the Acropolis’ largest temple was horizontally bowed so that it didn’t seem to sag, and that explanation persisted for millennia. New research suggests a different reason

Sonja Anderson | Daily Correspondent

September 18, 2026 1:11 p.m.

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Athens’ ancient Parthenon, the most famous of all Greek temples, looks like a perfectly rectangular structure, bolstered by Doric columns and topped with crumbled triangular friezes. In reality, the 2,500-year-old building contains almost no straight lines or right angles. 

People have long believed that Athenian architects gave the Parthenon subtle curves to create a consummately linear optical illusion. But according to a study recently published in Royal Society Open Science, that assertion is “one of the oldest and most enduring myths in human history.” 

“It’s widely accepted that it was made this way on purpose,” study author Alain Goriely, a mathematician at the University of Oxford, tells New Scientist’s Chris Simms. “But there is strictly no evidence that the refinements in the Parthenon actually produce the proposed visual illusions.” 

Goriely has examined four “myths” surrounding the Parthenon’s structure, focusing on its curved horizontal elements, column entasis, larger corner columns and proportional adjustments. The mathematician, who is experienced in applying math to biology and engineering, maintains that although these physical attributes exist in the Parthenon, they weren’t meant to trick the eye.

The Parthenon’s stylobate, the top layer of its rectangular base, has “a slight deliberate upward curvature,” Goriely writes. We know this because of careful measurements taken in the 19th century: The middle is a little over two inches higher than the sides. And that upward curve is detectable not only on the stylobate, but on the euthynteria—the upper foundations, located underground—and on the entablature, which sits atop the columns. The longstanding assumption is that these elements were purposefully curved because if the lines were straight, viewers would perceive them as sagging downward. 

“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 realize that the effect does not appear,” Goriely tells New Scientist. “And although it might work on paper, the effect in the real 3D building with an observer is completely different.” 

But if the curve wasn’t inserted to correct the Parthenon’s appearance, why did architects Callicrates and Ictinus include it in their fifth-century-B.C.E. designs? Neuroscientist Marge Livingstone, who researches visual perception at Harvard Medical School, tells New Scientist, “I think it must have been for drainage, just like on roads.”

The myth about the Parthenon’s horizontal curvature can actually be traced to ancient times. In the first century B.C.E., the Roman architect Vitruvius asserted that the Parthenon’s designers knew its lines would appear to curve downward if they were perfectly straight. Vitruvius’ claim was absorbed into Parthenon lore. Goriely isn’t the first to question it. 

“Vitruvius would seem to be assuming that the architects of the Parthenon wanted the Parthenon to look perfectly straight—wanted its lines to look perfectly horizontal and perfectly vertical,” art historian Jeffrey Hurwit, an expert on Acropolis architecture, told PBS in 2007. “I think there are good grounds to question that.”

Another structural element Goriely tackles is the Parthenon’s bulging columns, which demonstrate an architectural technique called entasis. Standing nearly 35 feet tall, each scored column bulges about an inch at its middle. People have long believed that this was to account for an optical illusion that, were they even, would make them seem narrower in the center. 

Nonsense, Goriely contends. He writes, “The assertion that straight-sided shafts appear concave lacks empirical support, and, to my knowledge, no such illusion has ever been scientifically demonstrated.”

Swollen columns are common among Doric temples like the Parthenon, but experts don’t know exactly why. Hurwit told PBS, “The slight swelling makes the columns seem to be tense; they seem to swell up to respond to the weight that they carry. In fact, entasis is the Greek word for tension or swelling.” 

Livingstone, for her part, tells New Scientist, “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.” 

The Parthenon’s corner columns are also just over an inch and a half wider than its other columns. Vitruvius once said this was so that they did not appear narrower because of another optical illusion. For his study, Goriely analyzed the established irradiation illusion—which has to do with foreground and background brightness—and found insufficient evidence that it applies to the Parthenon’s columns. 

The final myth has to do with the Parthenon’s frieze—the carved panels in its upper level. It contains human figures with heads that are slightly enlarged when measured against modern head-body ratios. Some experts have claimed that the sculptor Phidias made them larger so that viewers on the ground—whose eyes are nearer to the figures’ feet than to their heads—would perceive the bodies as proportional. Goriely, however, concludes that ancient Greeks’ body-head ratios were simply different from modern people’s, given how much shorter they were on average. 

The Parthenon’s architectural quirks, then, weren’t attempts to correct illusory optics—but matters of practicality or aestheticism. Phidias was the artistic director of the project, and Hurwit once guessed that the Parthenon’s entasis and curvature may have been his doing. 

“These deviations from the straight, from the perpendicular, from the perfectly vertical, from the perfectly horizontal are analogous to the curvatures and the swellings and the irregularities of the human body,” Hurwit told PBS. “And in that sense, the Parthenon strikes me as being a sculptural as well as an architectural achievement.”

Sonja Anderson is a daily correspondent for Smithsonian magazine who covers art, archaeology and culture, from newly discovered artifacts to the latest art heists.