Entasis (pronounced en-tuh-sis)
(1) In architecture, a slight convexity given to
a column or tower, claimed to correct the optical illusion of concavity and create
the perception of straight lines.
(2) In medicine and physiology, an involuntary or
spasmodic muscular contraction (also called entasia (from the Greek ɛnˈteɪzɪə)).
(3) In typography & calligraphy, the thinning in the waist of a stroke, the technique used to compensate for the visual perception of a stroke with perfectly straight sides appearing slightly to bulge.
1745–55: From the Latin entasis, from the Ancient Greek ἔντασις (éntasis) (tension, straining), from εντείνω (enteínō) (to stretch or strain tight), the construct being enta, variant stem of enteínein (to stretch tight) + teínein (to stretch) + sis. The –sis suffix was from the Ancient Greek -σις (-sis) and was attached to words in English often via Latin or French. It was identical in meaning with the Latin –entia and the English –ing and was used (1) to form nouns of action or process (catharsis, dialysis, diagnosis, crisis etc), (2) in medicine to form nouns of condition (psoriasis, sepsis, tuberculosis, psychosis etc) and more generally (3) nouns as required (basis, oasis, thesis, stasis etc). Entasis is a noun; the noun plural is entases.
The Entasis or Parthenon Principle
In modern architecture, entasis is the
application of a convex curve to a surface for aesthetic purposes. Its best-known use is in the columns from
antiquity which curve slightly as their diameter is decreased from the bottom
upward. Because no relevant documents have yet been discovered, it’s not known whether the architects in antiquity applied the technique for aesthetic effect or as an engineering technique to enhance strength. The
latter is suggested by the design principle being described by Roman architect
Marcus Vitruvius Pollio (circa 75 BC–circa 20 BC) using the Greek word enteino (to stretch or
strain tight), suggesting some emphasis on structural strength rather than
appearance. However, until contemporary records are uncovered, their reasons for using entasis remain mysterious, hence the two-thousand odd years of conjecture.
The Second Temple of Hera (circa 55 BC) was built in the Doric order, just north of the first. For the visual effect of entasis to work, the convex curve has to be so slight as to be imperceptible and it's not known why the Second Temple of Hera has an entasis so pronounced the curvature is obvious; there is illusion of straightness. The proportions are such that historians have speculated it must have been deliberate (presumably for structural strength) but it's at least possible the architect was afflicted by the desire many of his modern contemporaries share: The wish to produce something "original" and "new", the reason why so many modern buildings are so unpleasing to the eye, architectural awards & prizes handed out not for beauty and elegance but novelty and shock.
For millennia, entasis and its place in the history of architecture has been one of the most persistent tales from Antiquity but there have long been contrarians prepared to argue the concept, while not exactly a myth, is greatly exaggerated in significance. In September 2026, Belgian mathematician Professor Alain Goriely (b 1967; professor of mathematical modelling at the University of Oxford) published the findings of his study, challenging the belief the Parthenon’s “curves” were included to correct “optical illusions” that would have made pure straight lines appear “distorted”. What the professor’s modelling was said to reveal was (1) the “curves” are practically imperceptible and the alleged “illusion” they were claimed to correct doesn’t exist; “the illusions are illusory”. Deconstructing Vitruvius, the study begins with the claim the sides of the Parthenon’s stylobate (base) are not horizontal but form a very flat “V”, rising gently 60 mm (2.36 inches) towards the centre. According to Vitruvius, this was to correct the illusion that, when viewed as a whole, the base appears to “sag in the middle”. For centuries, the “sagging effect” was attributed to one of two “tricks of the light”: (1) That because of the way light is interpreted by the human brain, long horizontal lines “appear to slump” towards the centre or (2) That the structure’s marble columns create the illusion; this based on the “Hering illusion” (where in 2D (two dimensions) parallel lines can appear “bowed” when intersected by other lines). Professor Goriely found nothing to support either proposition, noting the Hering illusion (discovered in 1861 by German physiologist Ewald Hering (1834--1918) is most apparent when lines intersect at acute angles and the Parthenon’s columns are anyway “too close to the vertical” to produce the illusion. Additionally, extensive modelling produced no proof the effect would manifest on the Parthenon even in 3D (three dimensions), viewed from any angle.
The persistent claims of entasis.
Those details were really footnotes in architecture textbooks, entasis the most famous of the legends. What that suggests is “bulges” in the Parthenon’s columns (the curvature called entasis) were included by the builders to correct an optical illusion that would make them appear “too narrow” in the middle. Not only did Professor Goriely found no evidence the illusion exists but the columns bulge by a mere 18 mm (less than ¾ inch) which, at that scale, is simply not perceptible to the human eye at a typical viewing distance. What he doesn’t dispute is the architects may have had some reason to include variations in the dimensions; it’s just he found no evident they were there as “optical correctives”, the slopes on the base perhaps there for a reason as mundane as preventing puddles forming after rain; as every builder knows, only a very slight incline is needed for water to flow. The very minor increase in width in the columns’ centre sections is more mysterious and may have been something to do with what would have been a very labor-intensive production process but there seems to be no optical effect.
Beyond the math, Professor Goriely speculates the reason the myth has proved so enduring was the extraordinary level of veneration granted to the engineers, philosophers and architects of Antiquity when, in the late Medieval period and (especially) the Renaissance, so many of the texts were “re-discovered” and a the perception emerged of Ancient Greece as a supremely knowledgeable and ingenious civilisation. For centuries, in Western Europe, the Classical World was idealized and unless explicitly disproved (as came to be done of their medicine, cosmology and such), the texts were treated with great respect, thought something of “Civilization’s gold standard”. In the modern age, the veracity of what Vitruvius wrote tended to be reinforced by internet users repeating the tale, search engines affording a greater credibility to “facts” appearing in the greatest volume. Now of course, AI (artificial intelligence) bots have centuries of architectural texts from which to harvest information and given what Vitruvius who wrote about the Parthenon (400 years after its construction), came to be treated as something “scriptural” (despite the loss of loss of the many Greek texts about their temple architecture he claimed to have read when preparing his own), the authority was strengthened. Untypically for an academic paper, the professor recommends not too much dwelling on his findings but commending instead: “Trust your own eyes, question what you see and decide for yourself whether the theory of optical corrections holds up.” Professor Goriely concluded entasis “might be the oldest myth that we have” before mischievously adding “apart from religion.”
1964 Rolls-Royce Silver Cloud III Flying Spur; coachwork by H.J. Mulliner Park Ward.
One orthodoxy to emerge in the twentieth century was the famous Rolls-Royce radiator grille owed as much to Classical architecture as to being something there to prevent stones damaging the fragile core behind; if Rolls-Royce was going to be influenced by anyone, it’d be the architects of Antiquity. According to chapter 4 of The Lexicon of Rolls‑Royce (the company doesn’t have web pages, it has chapters), what it styles as the “Pantheon Grille” was “…inspired by Rome’s imposing Pantheon temple, the Rolls-Royce grille is iconic. The Pantheon’s majestic columns were purposefully built with wider middle sections so that the human eye perceives each long pillar to be completely straight. It’s a perfect optical illusion and a genius stroke of design. Taking inspiration from this, the Rolls-Royce grille is tactfully arranged using wider columns at the edge and thinner columns towards the middle to create an aesthetic illusion of symmetry when admired from the front. It’s a design that appears more perfect than nature intended.” The days are gone when Rolls-Royce’s documents were characterized by understatement (it once described its engines’ power outputs as “adequate”), the vulgar numbers revealed only when German regulators humorlessly insisted.
While Professor Goriely’s computer models could find no evidence of the effect, a century-odd earlier, Rolls-Royce’s designers were convinced by the optical tricks of the Greeks and in 1925 integrated one of their optical techniques their new grille. Although the “squared-off” shell dates from shortly after the company’s formation in 1904, not until 1928 did the now familiar grille with its upright bars become standardized. Prior to 1925, the radiators were fronted by horizontal “slats” best thought of as “louvers” in that they functioned like “venetian blinds” (controlled by a lever next to the driver) to enable the airflow to be controlled (thus regulating engine temperature). By the time of the release of the model Twenty in 1928, improvements in thermal-management technology meant the slats were no longer needed so the designers could start with a “clean sheet” and, being Rolls-Royce, the went neo-classical and built their own Pantheon, refining the ideas first seem in 1925 on the “New Phantom” (known retrospectively as the “Phantom I” (1925-1931) after new generations of the model followed). So, although Professor Goriely’s math couldn’t detect any evidence entasis produced a detectable effect for those looking at the Parthenon, what Rolls-Royce does has been modelled and although slight, the effect of their trick is real.
Lindsay Lohan in Rolls-Royce Phantom Drophead Coupé (2007-2017). By the 1970s factory (mostly) had ceased to use the historic terms FHC (Fixed-Head coupé) and DHC (Drop-Head Coupé (DHC) and the revival in 2007 for the Phantom Drophead Coupé has proved (thus far) a nostalgic one-off. Over the decades, the designers generally were successful in their adaptations as they were required to make the grille wider and lower but the Phantom would have benefited aesthetically if a more traditional approach had been taken with the headlamps (centre) and even hidden units (right) would have been more pleasing. Still, twenty-first century customers seem more accommodating of stylistic innovation than earlier generations.
According to opticians, what the design does (wider bars at the edges, more slender towards the centre) is create the illusion of symmetry when viewed straight on (at even a slight angle there will be no effect). That’s said to be because when viewing such a structure, the brain processes the image as a whole (not a sequence of individual bars) and, paradoxically, what the slight difference in width does is render an “artificial equalization”. Because of the way the brain processes the sight of a series of “parallel bars”, were they equally-spaced and equally wide, there would be a “hollowing” effect with a “pinching” towards the centre, caused by the natural human tendency to perceive outer edges as tapering away. The eye is an outgrowth of the brain and it’s the brain doing the processing; while “looking at a grill” might sound a simple task, in the Rolls-Royce grille there’s a lot of “information” and processing it all is an act of high-level cognition.
All else being equal, the brain tends first to focus on an image’s centre (that information sent to the fovea centralis (the part of the retina handling “sharp central vision”)) with the edges simultaneously entering the “peripheral vision” where spatial resolution decreases (the brain therefore gathering less precise detail about the outer dimensions). All this happens in a fraction of a second but does still happen sequentially, the brain using “predictive modelling” to “fill in the blanks” and there is much to process, the grille a large, highly reflective three-dimensional object with repeating lines. The brain’s visual cortex has much to do understand the contrasting light patterns and depth cues and that it does all this in a fraction of a second in an indication of how powerful a machine it is. Additionally, Rolls-Royce further assists the brain in “manufacturing perfection by machining each bar with a very slight outward curve, not detectable to the naked eye. The combination of this functionally imperceptible “width-shifting & curvature” uses the way the brain operates to induce the required corrective “shortcuts”.
The Pantheon Temple, Rome (left) and 1985 Rolls-Royce Camargue (right).
The Pantheon's Latin inscription M·AGRIPPA·L·F·COS·TERTIVM·FECIT isn't all that poetic and reads like a note the draftsman might have put on the blueprint (had there then been blueprints): it translates as "Marcus Agrippa, son of Lucius, made [this building] when consul for the third time.", crediting the Roman statesman & general, Marcus Vipsanius Agrippa (circa 63 BC–12 BC) who commissioned the construction during his third consulship in 27 BC. The Pantheon that stands today was rebuilt by Emperor Hadrian (Publius Aelius Hadrianus, 76–138; Roman emperor 117-138) circa 126 AD after the original structure suffered severe damage in a blaze; Hadrian chose to retain Agrippa's inscription as a tribute (not all the emperors were narcissists). Since 609 AD, the Pantheon has been a Roman-Catholic church and is known as the Basilica Santa Maria ad Martyres (Basilica of St. Mary and the Martyrs). In 1975, when the Camargue (1975-1986) was released, the novelty of it being the first Rolls-Royce designed using exclusively metric measurements (except for the odd carry-over component) attracted little attention but there was much comment about it being the first built with anything but a perfectly vertical grille. The Camargue's grille was slanted at a (for mid-century Rolls-Royce) rakish 7o.
Waftability
Understandably, the malapropism “Parthenon grill” is sometimes heard (and there is a well-reviewed Greek restaurant in Murfreesboro, Tennessee of that name) and despite occasional claims, the Pantheon grille doesn't feature a classic entasis (slight swelling in the middle of a column to counteract the alleged illusion of concavity) but the slight curve of the bars is real and can be checked with equipment no more complex than a “straight-edge” (a 12 inch (300 mm)) metal ruler ideal for the purpose. Although for much of the twentieth century Rolls-Royce was much associated with straight lines (the “knife-edge” models bodied by coach-builder Hooper between 1935-1959 the high point of the brief era of blending of a severe rectilinearly with the flowing lines of the pre-war aesthetic although, despite the mix, the approach was not within the lineage of post-modernism) curves have often been a component and in 2009 Tom Purves (b 1949; CEO of Rolls-Royce Motor Cars 2008-2010) announced the neologism “waftability” was “the essence of the brand”. That, he defined as “calm perfect motion and accelerating quickly without fuss”. Back then (and 2009 seems now little less remote than the days of the Cold War (1947-1991)), the CEO was describing the relationship between the appearance of a static Rolls-Royce as something that embodied that definition, revealing the internal name for the “gentle, upswept line of the sill” on the new Ghost model was a “waftline” (actually borrowed from the fashion business), the idea being it created “a powerful, poised stance and makes the car appear to be moving when stationary.”
The significance of “waftability” was Rolls-Royce was then still in the business of making large-displacement engines running on fossil fuels sound and behave as if they were electric motors but, by 2023, the company announced the Spectre, the brand’s first purely electric car. So it had taken a while but the interest in electric energy predated even the formation of the company in 1904. Sir Henry Royce (1863–1933) was an engineer who had designed dynamos, electric crane motors and patented the bayonet-style light bulb fitting while Charles Rolls (1877–1910) as early as 1900 drove an electric car declaring it the almost ideal form of propulsion, observing: “The electric car is perfectly noiseless and clean. There is no smell or vibration, and they should become very useful when fixed charging stations can be arranged. But for now, I do not anticipate that they will be very serviceable – at least for many years to come.” So it proved. By 2023 however, the technology was ready and so (more debatably) was the infrastructure and there is nothing better at waftability than something large, luxurious and electric, Rolls-Royce saying that some time in the next decade, their last car running on fossil fuel will leave the assembly line. Nothing lasts forever and, having spent more than a century trying to make ICEs (internal combustion engine) as smooth and silent as electric motors, the times seem now to suit Rolls-Royce. For others (such as Ferrari, Porsche, Dodge etc), selling to a customer base with an emotional attachment to the howl, throb & scream of gasoline (petrol) exploding in six, eight or twelve combustion chambers, the challenge is to find a way to make them content with a piped soundtrack. Engineers have conquered matters of performance and even range but nostalgia may prove harder to package. For Rolls-Royce however, the task is simpler because it’s purely visual: While an electric car needs no radiator and thus no protective grill, it can be guaranteed Pantheon Grilles, severely cut in stainless steel, will continue to appear.

























