simple vault construction. In their rectangular and circular temples we find the origins of the religious types

of the Roman Em

pire.

In the history of Art, Roman architecture is of the greatest importance, because it is the fountain head out of which the style of the Early Christian, Medieval, Renaissance and Modern eras were developed. It forms the connecting link between the practise of subsequent ages and

the experimentations and perfections of the various peoples with whom the Romans came in contact. It must not be thought that Rome served as an artistic clearing house for the earlier arts and was wholly devoid of originality. It is true that many of her decorative elements were derived from Greek sources, but even in this field many innovations are found. As innovators on the structural side they contributed to the resources of the designer the groined vault and dome, derivatives of the arch which remade the science of planning, making possible the substitution of vast, open interiors, for the column encumbered halls of Egypt and the narrow structures of Greece, for in all of these earlier constructions the unobstructed areas were limited by the restriction of the lintel.

The Etruscans employed the arch principle in the construction of barrel vaults (a continuous arch roofing the space between parallel walls). The preservation of the Eternal City is due to a vaulted work of this kind. Under the direction of Tarquinius Superbus (500 B. C.), the tyrant of Etruscan birth, whose oppression led to the abolition of regal rule, the great Cloaca Maxima (Fig. 1.) was built. This "Great Sewer" drained the area between the Palatine and Capitoline hills and to the present day, so carefully was it constructed, it still discharges its waters into the Tiber in the vicinity of S. Giorgio in Velabro. It will be seen that the stability of a barrel vaulted fabric (Fig. 2.) depends upon the massiveness of the supporting walls and as long as the simple barrel vault was used there was no possibility of laterally developing the construction. The possibility of intersecting a barrel vault with a second one at right angles to the first, suggested itself. (Fig. 3.) The lines of intersection (Fig. 4.) or groins of the two vaults, normal to each other, thus had a common base upon which was concentrated the weight and thrust of both

vaults. When several bays of groined vaulting are placed together the thrusts of the arched ceiling of quadripartite vaults were concentrated upon a series of isolated supports or piers instead of being resisted by cumbersome walls which therefore became structurally unnecessary. The invention of groined vaulting freed the Roman plan from the restrictions of limited areas and made possible the majestic and imposing structures of imperial Rome so admirably adapted to the times. The introduction of vaulted ceilings, also freed the monuments from the possibility of destruction by fire, a menace that is ever present in wooden trussed construction. An idea of the stupendous character of this type of building can be gained by contrasting the Great Hall of the Ammon-Ra Temple at Karnak (Fig. 5.) with the tepidarium of the Baths of Diocletian (Fig. 6.), Rome. In the Egyptian edifice the broadest aisle is twenty feet wide while the uninterrupted floor space of the tepidarium of the Themae of Dioletian is 340 by 87 feet.

Having achieved a method of constructing their monuments, the Roman architects evolved a system for relating the various elements of their complicated schemes to ensure a balanced and unified plan, with carefully expressed axes and well considered vistas. (Fig. 7.) The great central halls (Fig. 6.) were lighted by huge lateral windows carried up to the full height of the vaulting, their sills being determined by the highest part of the roof of the subordinate apartments that were grouped around the important rooms. The employment of this clerestory scheme resulted in exterior effects of great variety and interest which adequately and truthfully echoed the various functions of interior distribution. The masses of the exterior were disposed with the same regard for the laws of symmetry that controlled the arrangement of the plan and universally resulted in effects of great dignity and order.

Symmetry was the dominant law of Roman composition and in its employment the designer was certain to achieve results that everyone could understand. Horizontal

Ground Plan of Baths of Caracalla, Rome. AA. Entrance Halls; B. Central Vaulted Hall; C. Unroofed Bathing Pool; D. Domed Hall with Hot Bath. (Note general symmetry.) (Fig. 7.)

dual symmetry (bilateral symmetry) has an esthetic value in that it accords with the normal habits of vision developed by the environment, and designs laid out in deference to its laws make an immediate appeal to all people. To the more highly cultivated esthetic sense, proportion is more pleasing than symmetry because it is susceptible of more complex treatment. To the Roman, with his ideas of formal classification and organization, simple symmetry was the best method of portraying his racial characteristic.

A unified whole, made up of like and equally distributed parts may be taken as the canon of Roman architectural composition. It was essential that the works of the Roman architect should command attention through the qualities of colossal size, opulence of materials, and visible grandeur.

The delicacy and refinement that so well reflected the intellectual atmosphere of Attica would have been ineffective in expressing the overwhelming power and administrative formalism of the Empire.

Architecturally, the most important vaulted building of Rome was the Pantheon (Fig. 8.), built by Hadrian between 117-138 A. D. It consists of an hemispherical dome 142 feet in diameter supported upon a massive circular drum. A great oculus or round opening, twenty-eight feet in diameter at the top of the dome admits light into the temple and at the same time reduces the weight of the structure at its weakest point. (Fig. 9.) This aperture is open to the sky, but so great is its height (148 feet) that the most violent storms have but little effect upon the temperature of the interior. In bright weather the sun's rays dart through the opening and mark a great circle of light upon the pavement; in storm the rain falls slowly in the form of a humid cylinder. Architect and painter alike have felt the impressiveness of this great interior. When Michael Angelo painted the vault of the Sistine Chapel he placed his titanic figures against a background inspired by the sky vista that he so loved to look up toward in the Pantheon; later in his design of St. Peter's he stated that his aim was to raise the dome of the Pantheon upon a substructure of the form of the basilica of Constantine. A study of this same monument inspired in the Florentine architect, Brunelleschi, the idea which he executed in the construction of the dome of S. M. del Fiore of Florence.

The thick supporting wall (Fig. 10.) of the monument is pierced by eight, alternately rectangular and circular niches, one of which forms the entrance to the building. The hemispherical surface of the interior of the dome was treated with 140 coffers. The lower mouldings of these coffers are made wider than the upper ones in order to overcome the effects of foreshortening. Concerning the fabrication of these panels there has been a great amount of interesting discussion. Professor Hamlin has proposed