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 p124  Arcus

Article by Anthony Rich, Jun. B.A. of Caius College, Cambridge
on pp124‑125 of

William Smith, D.C.L., LL.D.:
A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.

ARCUS (also fornix, Virg. Aen. VI.631; Cic. in Verr. I.7; καμάρα), an arch. It is possible to give an arched form to the covering of any opening by placing horizontal courses of stones projecting over one another, from both sides of the opening, till they meet at the top, and then cutting the ends of the projecting stones to a regular curve, as shown below. This form is found in the most ancient architecture of nearly all nations, but it does not constitute a true arch. A true arch is formed of a series of wedge-like stones, or of bricks, supporting each other, and all bound firmly together by their mutual pressure.

A circle of stone wedges, meant to illustrate a stage in the construction of an arch. It would seem that the arch, as thus defined, and as used by the Romans, was not known to the Greeks in the early periods of their history, otherwise a language so copious as theirs, and of such ready application, would not have wanted a name properly Greek by which to distinguish it. But the constructive principle, by which an arch is made to hold together, and to afford a solid resistance against the pressure upon its circumference, was known to them even previously to the Trojan war, and its use is exemplified in two of the earliest buildings now remaining — the chamber built at Orchomenus, by Minyas, king of Boeotia, described by Pausanias (IX.38), and the treasury of Atreus at Mycenae (Paus. II.16). Both these works are constructed under ground, and each of them consists of a circular chamber formed by regular courses of stones laid horizontally over each other, each course projecting towards the interior, and beyond the one below it, till they meet in an apex over the centre, which was capped by a large stone, and thus resembled the inside of a dome. Each of the horizontal courses of stones formed a perfect circle, or two semicircular arches joined together, as the subjoined plan of one of these courses will render evident.

An engraving of a long narrow passage with a ceiling in the shape of a pointed vault. It is a view of a passageway in the walls of Tiryns, Greece, an illustration of the false vault. It will be observed that the innermost end of each stone is bevelled off into the shape of a wedge, the apex of which, if continued, would meet in the centre of the circle, as is done in forming an arch; while the outer ends against the earth are left rough, and their interstices filled up with small irregular-shaped stones, the immense size of the principal stones rendering it unnecessary to continue the sectional cutting throughout their whole length. Indeed, if these chambers had been constructed upon any other principle, it is clear that the pressure of earth all around them would have caused them to collapse. The method of construction here described was communicated to the writer  p125 of the present article by the late Sir William Gell. Thus it seems that the Greeks did understand the constructive principle upon which arches are formed, even in the earliest times; although it did not occur to them to divide the circle by a diameter, and set the half of it upright to bear a superincumbent weight. But they made use of a contrivance even before the Trojan war, by which they were enabled to gain all the advantages of our archway in making corridors, or hollow galleries, and which in appearance resembled the pointed arch, such as is now termed Gothic. This was effected by cutting away the superincumbent stones in the manner already described, at an angle of about 45° with the horizon. The mode of construction and appearance of such arches is represented in the annexed drawing of the walls of Tiryns, copied from Sir William Gell's Argolis. The gate of Signia (Segni) in Latium exhibits a similar example.

The principle of the true arch seems to have been known to the Romans from the earliest period: it is used in the Cloaca Maxima. It is most probably an Etruscan invention. The use of it constitutes one leading distinction between Greek and Roman architecture, for by its application the Romans were enabled to execute works of far bolder construction than those of the Greeks — to erect bridges and aqueducts, and the most durable and massive structures of brick. The Romans, however, never used any other form of arch than the semicircle.

Thayer's Note:

You will have noticed that the main thrust of this article is an attempt to make the Greeks invent the arch, or at least absolve them for not having done so. This is typical of a certain strand of thought, usually found among classicists, which can be baldly expressed like this: the Greeks were the source of all that is worth anything in the culture of the ancient Mediterranean, and the Romans were merely borrowers and imitators. And so in this article we have the logical conclusion of this mental process, in which, incredibly, an article on the vault, a characteristically Roman structure of which there remain thousands of good examples, is illustrated by two Greek structures, neither one of which is a vault!

Now maybe the Romans did imitate and adapt a lot, but in the case at hand, there is a vast difference between laying down a fitted circle of stones horizontally, packed in earth, and setting half of one upright to support, as our author puts it, superincumbent weight: it is the difference between dealing a game of solitaire flat on a table and building a house of cards. . . .

There is also a vast difference between building an arched doorway and realizing that the principle can be extended to cover very wide spaces without requiring an intrusive forest of pillars.

Finally, from the arch to further developments, in which the inventiveness of Roman architects cannot be denied, is a bold leap: yet our author does not mention that the proper understanding and construction of an arch is what underlies the vault — an extension of the arch along a straight line — and the dome, an even more innovative extension of the arch, in which it is rotated thru 180 degrees. Until the advent of radically new materials in the mid-twentieth century, these were the best methods of creating very large architectural spaces. (Nor is there an article in Smith's Dictionary for either the Vault or the Dome.)

This article also misses an opportunity to provide a clear explanation of how the arch works and why it can bear so much more weight than other systems for spanning interior spaces. The author is a classicist rather than an engineer.

(On this one I too will pass for now — alleging time constraints and a need to get basic information online first — but I hope to come back to this point. Very simply, the true arch, made of wedge-shaped blocks, takes advantage of the fact that wedges are like mules: the more you push on them, the less they move.)

Postscript: For about a year, had you landed on this page from a search engine called Looksmart, you would have read their capsule of this page: "Read an article on the structural innovations of the Greeks on the arch." If after reading the article, that capsule made no sense to you, congratulations: you formed your own opinion and you know that not every grown-up is right, nor everything you see in print. Looksmart eventually changed their blurb, by the way; then finally retired to their real line of business, pay-per‑click advertising.

If on the other hand you believe that that was an accurate summary, you're in deep trouble . . . and you should go back to the top of this page and read the article again — carefully this time.

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Page updated: 19 Oct 12