A reference to Figs. 98 and 99 will show the radically different appearance given by thus applying an Order of architecture as an ornament upon the face of a method of construction complete in itself. In Fig. 98 is shown a simple arcade supported on plain piers (A, Fig. 100); and in Fig. 99 is drawn out a similar arcade ornamented by the application of the Doric Order to the face of these plain piers, after the fashion shown in plan at B, Fig. 100.
This use of the Order produces an effect very different from that of the one or two examples of the use of attached columns already ex isting in Greek architecture, although it is probable that these may have suggested the application of the column to the face of a plain wall; a method of which the Romans had already availed themselves in the Temple of Fortuna Virilis at Rome. This example may easily have been copied from the similar use of the Order in the large Temple of Jupiter Olympus at Agrigentum, or in the Monument of Lysicrates at Athens.
In both these Greek structures the columns are apparently planted against the face of a connecting curtain wall. As a matter of fact, the columns are entire in both these buildings, the wall itself being built up between and behind them, with the face hollowed out so as to receive the shaft, thus suggesting the addition of the wall at a later period as a screen between the columns without affecting the lintel principle upon which the building was probably first de signed. In the Temple of Jupiter Olympus, the addition of this wall was probably made necessary by the fact that the tremendous scale of the building made the span covered by the lintel of a length too great to be carried safely in this fashion, and so the wall was introduced as an additional method of support. Possibly something of this feeling may have caused the use of the wall between the columns in the Mon ument of Lysicrates, though for different reasons. The plan of this monument being circular, it may have been thought that the overhanging projection of the en tablature between the supporting columns would weaken the lintel, either actually or apparently, so that it might require additional sup port at its point of greatest projection.
But the difference between the use of the column in this fashion, attached to a plain curtain wall, and its use placed against the face of a pier between arches, as the column was employed in the arcades of the Tabularium and later in the Theater of Marcellus and the Colosseum, suggests a great advance in the architectural effectivenesss of its use and in its close identification with the more constructive architecture of the Romans, even though there is but slight difference in the prin ciple of its application.
But in any event, the column, as thus used by the Romans in their architecture, can seldom be considered as an important struc tural feature. It does not even act as a buttress to resist the thrust exerted upon the exterior walls by the interior arches roofing the rooms or corridors.
The Romans must first have used a continuous and purely struc tural arcade of arches turned against each other and resting on heavy masonry piers, as in their aqueducts (Fig. 101 ). This undoubtedly proved monotonous in effect; and so the colonnade was simply grafted upon its surface, the columns being each placed against the center of a pier. The colonnade shown in Fig. 99, drawn according to the rule of Vignola, would be more pleasing if the plain surface in the bay between the three-quarter-engaged columns—below the en tablature and above the line of the necking had been omitted, thus allowing the lower line of the entablature to be dropped to the height of the horizontal line shown directly over the archivolt or backhand of the arch.
Use of Superimposed Orders. Aside from their assimilation of the arch principle from the Etruscan builders, and their use of the Greek-developed Order as a mere ornament applied on the face of an arch-supported wall, the Romans further varied—in one important particular—their employment of the Classic Order. 'Where the Greeks, almost without exception, had used one column—even of gigantic size where necessary—to carry from a low basement or stylo bate to the entablature that acted as the crowning member of the build ing, as well as of the Order used on its exterior facade; the Romans did not hesitate to superimpose one Order upon another, making two or more stories, one over the other, each carrying a complete Order upon its face. The derivation of this idea is possibly traceable to some of the Greek temples, in which a second Order was sometimes used on the interior to support the gabled roof covering the structure, and, incidentally, to admit of a higher central aisle. For this purpose they used either small columns, as at Pæstum (the Order is here the same in style and treatment as the one below, being merely smaller in scale), or, more often, a human figure placed upon the face of a plain pier. The idea of superposition, as developed by the Romans, soon became an important part of their architectural treatment; and in the later revival of Roman architecture which occurred during the Renaissance, this, method of treatment was frequently used.