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In proportioning the architrave, frieze, and cornice, care must be taken that no more is laid upon the columns than their own bulk: when the latter are one diameter apart, this quantity will be greater in height than when they are further distant; so that the greater the intercolumniation, the lighter in appearance will be the entablature, the columns still bearing the same weight, nor need they be increased after it is ascertained that they are competent to their duty: to do so would be to employ material in excess, which it should be the aim of an architect to avoid.
If we now examine the portico of the Pantheon, we cannot fail to perceive the agreement existing between the parts supported and their supports. The mean diameter of the columns is
7 Their height, including capital and base
46 5 The solid content of each
765 10-6 Consequently the cube of the whole 8 is
which leaves little more than 100 cubical feet of difference between one and the other; and if the crown moulding returned on the flank be comprised, the quantity contained in the entablature would equal that of the eight columns.
The pediment is omitted altogether in this calculation, it being in reality, though not in appearance, an additional load for the eight columns beyond their reguiar entablature, which is of marble, and weighs probably 452 tons; the granite columns with their marble bases and capitals are something more than that quantity, and these, including the entablature and pediment, probably contain upwards of 2000 tons of material.
The Capitals of the Columns of the Panthern are admitted to rank among the best examples found in Rome: though not so highly and elaborately worked as those which decorate the columns of the temple of (Jupiter Stator) the Dioscuri, yet they are remarkable for the
elegant arrangement of the ornaments: further details will be found in Taylor & Ciesy's Architectural Antiquities of Rome, whence the details here given have been selected
CAPITALS OP PANTHEON.
Fig. 1047. Although the Romans did not improve the arts which the Greeks had spread among them, by the introduction of the arch they materially altered the character of the architocture practised before the time of the Republic: this feature alone produced entirely
different construction, and the several changes it has since undergone in form have serrad to establish a variety of styles, as we shall afterwards find.
Sewers, aqueducts, bridges, theatres, amphitheatres, baths and triumphal arches, all exhibit the arch in its most useful application, and as did the halls of the baths vaulting of stupendous span; the dome of the Pantheon being 142 feet 6 inches in diameter internally, covered by a hemispherical dome.
Symmetry, as understood by Vitruvius, seems to relate more to the proportions of the façade than to those of the detail ; but he doubtless intended it to be understood that
perfect harmony should subsist between them as well as between each particular member, however subordinate; as in the well-formed human figure, all the limbs being in due pro portion, the whole when combined produces true symmetry : and the same author insists very strenuously on a careful study of the rules upon which this is founded, proving that the effect desired cannot be produced by a mere effort of fancy, or what is coinmonly called
A building, though entirely devoid of ornament, may be rendered beautiful by the justness of its proportion, and the richest edifice wanting in this never can excite admiration : façades having but height and breadth, these two dimensions must be equal to each other, if we adopt the symmetrical proportions prescribed by Vitruvius, for he observes * the square includes the human figure either lying down or standing in an erect posture, the arms being stretched out." Temples, triumphal arches, and other buildings left us by the Greeks and Romans were decidedly designed upon this principle, as were most of the façades of the religious structures erected since the fall of the Roman empire.
In the " Songe de Poliphile," originally published in Italian by Aldus in the year 1499, are some observations on setting out a façade, which convey some idea of the principles adopted for the formation of a perfect and harmonious design on the revival of Roman architecture.
* Draw a square figure, divided by three perpendicular and three horizontal lines, at equal distances from each other, forming sixteen squares ; on the top of the square add a half square, which, similarly divided, makes altogether twenty-four squares : in the lower square draw two diagonals, crossing eight squares in the same manner; then form a lozenge above the great square, tracing within it four lines on the four principal points that separate the four sides of the void."
After understanding this figure, I thought within myself what can modern architects do, who esteem themselves so learned without letters or principles? They neither know rules nor dimensions, and therefore corrupt and deform all sorts of buildings, both public and private, despising nature, who teaches them to do well if they would imitate her: good workmen, besides their science, may enrich their work either by adding to or diminishing therefrom, the better to please the eye, but the mass should remain entire, with which ali should be made to harmonise. By the mass is understood the body of the edifice, which, without any ornament, shows the knowledge and spirit of the master, for it is easy to embellish after any invention; the distribution and arrangement of the parts is also a matter of consideration; hence we may conclude that any workmen or their apprentices know how to ornament a work, but to invent lies only in the heads of the wise.
Taking from the square and a half, the lozenge and the diagonal lines leaves the three perpendicular and the three horizontal, except that in the middle, which terminates in the centre of the perpendicular, cutting it into four parts or portions ; by this rule will be found two perfect squares, one above and one below, each containing four small squares, which form the opening or doorway ; now if you take the diagonal of the lower square, it will show you what thickness must be given to the centre of the portico; if you carry it straight, the line will serve to denote the architrave : and the point of the centre of the upper square will show you the centre of the arch or curve to be given to the door ; turning a semicircle it will rest on the transverse line, which cuts the square and a half into two equal parts; but if done by any other means 1 do not esteem it perfect. This method was invented by ancient and expert masons, and observed in their arches and vaults, to give them both grace and solidity; the pedestal on which the columns rest commences at the level of the pavement by a plinth, and the whole is a foot high, furnished with mouldings; one portion is divided into architrave, frieze, and cornice, the latter being something more than the others; that is to say, if the architrave and frieze contained five parts, the cornice should be six. The whole twenty-four squares form a square and a half; then divide the upper half into six parts by five horizontal and five perpendicular lines, and draw a line from the centre of the fifth transverse to the corner of the great perfect square, where the architrave eommences; then draw it perpendicular on the key of the archivolt, and it will show you the height to be given to the frontispiece above, the extremities of which should unite and relate to the projection of the cymatium and its mouldings.
General Principles. - It would appear that all the principal Roman triumphal arches with single openings were a square, either comprising or excluding their attics : that the centre from whence the archivolt was struck was the centre of the square, or if the façade was more than a square, as the arch of Trajan at Ancona, then where the two diagonals crossed the centre was fixed. The width of the opening is generally half the entire extent, sometimes three parts out of seven.
These triumphal arches were generally surmounted by a group of figures, or the car and horses of the conqueror, accompanied by his companions in arms and the trophies obtained from the enemy; these, as shown on several medals, appear to be equal in height to of the entire edifice upon which they are placed, the attic and entablature representing }, and the columns and pedestals the other ş; and as the former are nearly equal in their height, it follows that the horse and his rider, or the car and its triumphant hero, were double the height of the pedestal on which they were placed, for so we may consider the attic which contained the inscription, the body of the arch being a perfect square, and in correct proportion, without the attic. The depths of these arches varied; that of Constantine at Rome is nearly the same as the width of the great centre opening; many of the others are less than that proportion; but it seems that the cube was the measure that
bounded the proportions, as shown in fig. 1053. The several Roman examples selected differ in arrangement, but not in principle, from the description given by Poliphile: take away the pedestals on which the columns
are placed, and then four squares in height include half the tympanum, and eighteen squares the entire figure, 6 of which may be considered as devoted to the arch, and the other 12 to supports : or, if we comprise the whole façade in 20 squares, and abstract the 8 which belong to the opening between the pedestals, we have 4 for each pier or sup
Fig. 1049. port, and 4 for the entablature, the supported being only 4 the quantity contained in the two supports: resistance to the arch, or its thrust, requires a different arrangement from that of a portico, but we nevertheless find definite proportions made use of, and a double quantity given to masses which have to bear weight as well as resist thrust.
The Arch of Augustus at Rimini has the height of its order determined by the length of the frieze.
The Arch of Augustus at Aosta resembles that of Titus in arrangement; it is a perfect square comprising the attic.
ARCH OF AUGUSTUS AT RIMINI.
AECU OF AUGI'STI'S, AT AOSTA.