348 ROMAN ARCHITECTURE. Part I. 227. Plan of Minerva Medica at Kome, as restored in Isabelle's " i!(lifices Circulaires," on the theory of its being a Bath. Scale 100 ft. to 1 in. This, however, is a polygon both internally and on the outside, and the mode in which the dome is placed on the polygon shows the first rudiments of the pendentive system, which was after- wards carried to such perfection by the Byzantine archi- tects,but is nowiiere else to be found in Rome. It prob- ably was for the purpose of some- what diminishing the difficulties of this construction that the architect adopted a figure with ten instead of eight sides. This, too, is, I believe, the first building in which buttresses are ap- plied so as to give strength to the walls exactly at the point where it is most wanted. By this arrangement the architect was enabled to dispense with nearly one-half the quantity of material that was thought necessary Avhen the dome of the Pantheon was con- structed, and which he must have employed had he copied that building. Besides this, the dome was ribbed Avith tiles, as shoAvn in Woodcut No. 229, and the space between the ribs filled in with inferior, ])erhaps lighter masonry, bonded together at certain heights by horizontal courses of tiles where necessary. Besides the lightness and variety Avhich the base of this building derives from the niches, it is 10 ft. higher than its diameter, which gives to it that proportion of height to width, the Avant of Avhich is the principal 228. Section of MinerVa Aledlca. Scale 50 ft. to 1 in. (From Isabelle.) 229. Rib of the Roof of the Minerva Medica at Rome.
