Antiquity: Optical Illusion & Aesthetics of Parthenon

Entasis in Antiquity

Refinements of architecture play an essential role in shaping the visual image and structure of the building. Refinements are conscious decisions made by the architects to revise the otherwise strictly straight lines of the building for aesthetic or practical reasons. Entasis, a slight convex curve of the shaft of a column, is a refinement frequently embodied by classical architecture. Many theories have been advanced to account for the implementation and purpose of entasis. The Parthenon, Temple of Hera, and Propylaea, which together exhibit varied forms and degrees of entasis, are prime examples of how entasis served its purposes in antiquity. Respectively, entasis corrects optical illusion, satisfies aesthetic needs, and enhances the functionality of architecture. The different applications of entasis reflect the unique ideas behind each building of its architectural purpose and its relationship to the surroundings. Prevailed in antiquity, entasis is an ingenious human invention that originated from our pursuit of both aesthetics and practicality.

Optical Illusion

Vitruvius, in his influential On Architectura, introduces the idea of optical illusion that the straight horizontal and vertical lines of post-and-lintel architecture appear to be curved when built on a large scale (figure 1. b).[footnoteRef:0] Whereafter, many scholars have connected the use of refinements with the correction of such optical disharmony. Entasis, by bulging the seemingly thinner section of the column from a perspective, cancels the concavity and “straightens” the lines of the building to eliminate the optical illusion. The brilliant architects Ictinus and Callicrates of the Parthenon incorporated entasis to balance the Parthenon which was built on uneven ground so that it shows perfect order and unity (figure 1.a). The diameter of the order decreases by a slight amount as the height increases in the upper ⅔ section (figure 2). As described in “Refinements on refinements” by Manolis Korres, “the first visitors to the Parthenon were certainly aware of entasis. ...however…their eyes could not immediately grasp the very subtle refinements applied to the Parthenon columns, which they often took to be straight (figure 3).”[footnoteRef:1] Without careful observation, the curvature of the columns of the Parthenon is indeed hard to perceive. The columns at peristyle have the entasis of 17.5 millimeters over the height of 9.56 meters, with a ratio of 1:546; the columns at east porch have a ratio of 1:383; the columns at west porch have a ratio of 1:493.[footnoteRef:2] The columns, with small refinements, appeared to be in straight lines. Thus, the architects’ pursuit of the appearance of perfect geometry is a pure correction of optical refinement rather than of any aesthetic means. Without entasis, the orders would have appeared with a concavity in the middle, showing imperfection and weakness. Such a pursuit of regularity and geometry is appropriate to the Parthenon for its purpose as the house of gods, which symbolizes authority, immensity, and perfection. In classical architecture, entasis of the orders, particularly the example of the Parthenon, allowed the architects to achieve harmony of form by the eye, correcting the optical illusion. [0: ] [1:] [2: ]

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Aesthetics

The application of entasis, however, seems not to be restricted to the correction of optical illusion in classical architecture. In fact, entasis are utilized to please the senses of the beholders for aesthetic reasons as well. “The greeks were not satisfied with the use of restricted rules or of a single rule as meant by Vitruvius…For the Greeks, the work was in its entirety a question of sensation.”[footnoteRef:3] In Paestum, the exaggerated use of entasis of the columns at Temple of Hera I is so visible to the human eye that it is impossible to claim the orders are constructed of straight lines. According to Frank Salmon in Cockerell and the Discovery of Entasis in the Columns of the Parthenon, at the Temple of Hera, the maximum extent of the entasis is 4.8 centimeters over a height of 5.5 meters with a ratio of 1/100.[footnoteRef:4] It exceeds the mere correction to become straight lines but rather inversely emphasizes the curvature of the columns. The columns of the Temple of Hera shape like cigars and mimic a muscular human body bearing a great weight with its organic shapes, analogous to the muscular details in the male statues of the classical period (figure 4).[footnoteRef:5] The exaggerated curvature is a personification of architecture comparable to the Greek ideology at the time. Entasis expresses a sense of dynamics and plasticity of Hellenism. Freedom of expression is conveyed through the variations of dimensions of the architecture. In addition, “the analogy between organic shapes and bearing structure is self-evident.”[footnoteRef:6] The Greeks were fully aware that “straight lines tend to create an oppressive and inflexible mien.”[footnoteRef:7] The purpose of entasis here is to give the column an organic structure and to avoid machine-made straightness, according to the aesthetics at the time. The Greeks and Romans were also admirers of nature, where they have found curved lines are the most beautiful forms.[footnoteRef:8] With the application of entasis, the continuing decrease of the diameter of the columns made Temple of Hera appear to grow taller, rising up from the ground with the majesty of Hera, as if it took root on Earth. Classical architectures are attempts to integrate human structures as a part of the living and organic nature while reconstructing the man-made idea of aesthetics. The utilization of entasis pleases the eyes of the viewers by relieving the rigidity of the straight line and perfect geometry while giving life and dynamics to the building. Such entasis is intended to be apparent and reflects the aesthetics of the building rather than compensating for the optical illusion. [3:] [4: ] [5:] [6:] [7: ] [8: ]

Practicality

Entasis could also be remarkably subtle, too subtle to be motivated by aesthetic concerns at all, but rather only for practicality. Athenian Propylaea, which has been measured at a maximum of 10 millimeters of entasis over a height of about 9 meters, shows a ratio of 1/900, far smaller than Temple of Hera and Parthenon.[footnoteRef:9] The invisibility of the refinement, therefore, indicates that the entasis is apart from optical correction and aesthetic motivation. Another example of the finest alteration in orders is that the section from the upper part of the orthostate to the lower part of the epistyle of the Parthenon had an entasis of about 2.7 millimeters, in comparison to its height of 8.9 meters with a 1/3300 ratio.[footnoteRef:10] This entasis is indetectable to the naked eye, more subtle than any previously known.[footnoteRef:11] Without modern technology, it would not have been discovered. Given the undetectability of the curvature, such entasis can hardly have served either to correct the optical illusion of the lines of the building or to stylize them. No aesthetic motivation seems adequate to explain these examples. The only possible explanation is that the curvature of orders sorely enhances the structural stability of the architecture, different from the two previous examples. J. Keller in The shape of the strongest column states that the strongest column is not strictly cylindrical, but rather “tapered along its length, being thickest in the middle and thinnest at its ends”.[footnoteRef:12] With refinements, the orders are strengthened to be more structurally stable and bear more weight. Thus, besides the optical correction and aesthetics, during the classical period, entasis enhances the functioning of the architecture, concerning only practicality. [9: ] [10:] [11: ] [12: ]

In conclusion, entasis, the building of orders, play various important roles in classical architecture. Examples of Parthenon, Temple of Hera, and Propylaea provide three different interpretations of the application and purpose of entasis---the pure correction of optical illusion, the alteration based on aesthetics, and the enhancement of practicality of the structure. It is not definite in which each entasis aims to achieve, but with its impact on the aesthetics and structure of the building, entasis is an essential feature in the prosperity of classical architecture.

Bibliography

1. Vitruvius, On Architecture, esp. books 1, 3, and 10.
2. Manolis Korres, “Refinements on refinements,” in Lothar Haselberger (ed.), Appearance and
3. Essence: Refinements of Classical Architecture: Curvature (1999), pp. 79-104.
4. Frank Salmon, C.R. Cockerell and the Discovery of Entasis in the Columns of the Parthenon
5. (2011)https://www.hoart.cam.ac.uk/Downloads/c-r-cockerell-and-the-discovery-of-entasiS-in-the-columns-of-the-parthenon
6. J. Keller, The shape of the strongest column. Arch. Rational Mech. Anal. 5 (1960), 275.

• Figure 1: 1.a. Parthenon as it visually appears with optical correction; 1. b. Parthenon as it visually appears without optical correction; 1. c. The actual form of Parthenon with optical correction.
• Figure 2: The orders of the Parthenon with entasis.
• Figure 3: Parthenon observed in a distance.
• Figure 4: The orders of Temple of Hera in Paestum with exaggerated entasis.