Perfect design or perfect myth?

In Athens, Greece, a temple has stood for over two thousand years. 

The Parthenon, dedicated to the goddess Athena, is famous for its “optical illusions.” Even though the temple barely has any right angles and straight lines, it still looks perfectly perpendicular due to subtle visual corrections our eyes make upon viewing.

It’s unknown whether these optical corrections were purposeful design choices of the Greeks, or if they were unintentional accidents that fortuitously occurred in the building process.

This use of optical illusions in architecture originated in The Ten Books on Architecture, a classic written by the Roman architect and engineer, Vitruvius. In this book, Vitruvius proposed several architectural alignments to create optical adjustments. One such alignment was to employ comparatively thicker columns in the corners of buildings.

In the Parthenon, the corner columns are built 2% thicker than other columns. Vitruvius explains that, because of the “unobstructed air around them” and how they are “sharply outlined,” corner columns appear thinner to onlookers than they actually are, therefore, it is necessary to correct this by increasing their thickness. 

Vitruvius's interpretation has been further explained by scholars. One widely accepted explanation is the so-called “irradiation illusion.”

When looking at the image above, we can see an example of this illusion. The white square on the black background appears to be larger than a black square on a white background, because the white object simulates adjacent regions in the visual field. The viewer, therefore, experiences an overstimulation in the adjacent regions, leading to the illusion of a larger white square.

However, not everyone agrees with this interpretation. Mathematician Alain Goriely, from the Mathematical Institute at the University of Oxford, claims that this optical illusion does not exist, or is largely ineffective.

Goriely finds that this correction would only work from certain viewpoints with very specific background conditions. That is, the viewer would need to see both the corner and the other columns at the same time, with the corner column set against a very bright sky background, mimicking the dark square, and the other columns against a very dark background, like the white square. 

In real life, the background of the columns is usually mixed with stones and shadows. Without these ideal conditions, he argues that the difference in the column thickness cannot be perceived clearly. Thus, if the goal of the Parthenon’s design was to make the columns appear equally thick, it would have been more effective to simply make all the columns the same thickness.

When standing at the positions highlighted in purple from the above image, observers will perceive all of the columns as the same thickness, therefore experiencing the optical correction explained by Virtuvius. At any other positions, however, the corner columns will be seen as thicker than other columns, which contradicts the idea of optical correction. 

Goriely suggests that the Greek’s motivation for these thicker corner columns could have been purely aesthetic, or an attempt to introduce dynamics to the structure, making the temple more organic. Given this and the fact that Vitruvius was writing almost four centuries later than Parthenon, a question arises: How much weight should we actually give Vitruvius’s explanation?

Professor Vittoria Di Palma, an architectural historian at USC, suggests we should not discount the Greek’s use of optical correction entirely. Although the corrections are indeed subtle and may not always be perceivable, she says, this alone does not dismiss the idea of optical correction.

“It is true that on the Parthenon those adjustments are incredibly, incredibly refined and not obvious at all. You can, however, look at other Greek temples, such as the Paestum. The temple of Hera is a much older building, but you can see things like entasis in that building,” she said. “We have examples of temples that utilize these optical adjustments.”

During her visit to the Parthenon, Di Palma learned that every block in the Parthenon is unique. To her, this phenomena shows signs of careful and intentional construction.

The debate of the optical illusion and its use in the Parthenon’s architecture continues. Even if someday in the future we are able to fully understand how the Parthenon was designed, and it is no longer mysterious, a new obstacle arises: whether or not the temple feels as powerful as it does today.

Di Palma believes the answer is yes.

“I think that architecture, great architecture, can incite a feeling of awe, even if we know everything about the way that it is made,” she said. “The quality of the workmanship, the sense that you get when you're standing in front of it, or when you're inside it, what happens with the light, the significance that it's had for the culture that created it: these are all things that can create a sense of awe, and in those cases, knowing more about what it is contributes to one's appreciation.”

The wonder that has inspired generations to visit and study the Parthenon comes from more than its myth; it also lies in its structure, its history, and its significance to a culture. Whether the question of optical illusion is ever resolved or not, the Parthenon itself will remain a masterpiece of human architectural achievement.