CIR

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CIRCUMFERENCE, the curve-line by which the areaof a circle is bounded.

CIRCUMFERENTOR, (Latin , circumferre ), an instru-ment used by surveyors in taking angles; it consists ofa brass circle and index, in one piece, commonly aboutseven inches in diameter, an index about fourteen incheslong, and an inch and a half broad. On the circle is acard, or compass, divided into 360 degrees; the meridianline of which answers to the middle of the breadth of theindex. There is also soldered on the circumference a brassring, on which screws another ring with a flat glass in it, soas to form a kind of box for the needle, suspended on a pivotin the centre of the circle. There are also two sights toscrew on, and slide up and down the index, as also a ball andsocket screwed on the under side of the circle, to receive thehead of the tripod or stand.

CIRCUMSCRIBE, to draw a figure round another; theone being rectilinear, and the other either rectilinear orcircular, with the sides of one touching all the angles of theother.

CIRCUMVALLATION, a round enclosure of trenches,or fortifications.

This word, from the Latin vallo, or vallum, denotes pro-perly the wall, or rampart thrown up, but as the rampartis formed by entrenching, and the trench makes a part of thefortification, the word is applied to both.

CIRCUMVOLUTION, (from the Latin , circumvolutus)the act of rolling round. In architecture, this term is appliedto the spirals of the Ionic capital; every turn of which iscalled a circumvolution. In the most ancient examples of theIonic order, the volute has three circumvolutions, or revo-lutions, as they are otherwise called; but that of the templeof Minerva Polias, at Priene , has four. See Volute, Spikal,and Ionic Order .

CIRCUS, in antiquity, a large enclosed space, adapted forchariot-races, an amusement to which the Romans werepassionately attached. The name Circus does not convey anexact idea of the form of this building, which both in itsoutline and its use resembled the Greek stadium.

There were many circi in Rome, of which the CircusMaximus, and the Circus Agonalis , were perhaps the largest.The former may still be distinctly traced ; the latter retainsits external form only in the Piazza Navona of Rome . Thisspecies of edifice appears to have been very early introducedamong the Romans, and, like many of the first public edifices,was of a temporary character, and constructed of wood.

The first permanent circus, at Rome , was said to have beenbuilt by Tarquinius Priscus , and was situated in a valleybetween the Palatine and Aventine hills. On this site wasafterwards erected the Circus Maximus , which was enlargedby Julius Caesar , and rebuilt and richly ornamented byAugustus. In the time of Nero it was burnt down ; Trajan repaired it, and increased its dimensions so much, as to con-tain the whole Roman people. The exterior of the circus,except at the carcera, consisted of two stories, adorned withcolumns, and finished with a terrace. The ground-floor wasoccupied by merchants, except on the days appointed for thegames. Augustus brought an obelisk from'Egypt 126 feethigh, and placed it in this circus. Constantius also erected init the obelisk now called the Lateran , which is the largest ofall the Roman obelisks.

The Flaminian circus was of considerable magnitude. Itsonly remains are ruins beneath the present pavement of theoity. There are several other circi, the ruins of which maybe traced; but that which demands our attention most, is thecircus of Caracalla , as very considerable traces of its ancientform are yet to be seen.

Several of the circi in Rome , were exteriorly surrounwith magnificent porticos, except on the side where ^career® were placed. Others were simply enclosed ^ ^a wall, pierced with doors and windows, as in the circCaracalla . The lower part of the circumference of the ^beneath the seats, together with the porticos, formedgalleries of arcades, or fornices ; serving in part for an a®to the staircases leading to the seats, and in part for the s ^of various traders. The staircases of different circivariously distributed, according to the judgment of the a ^tect. The principal staircases led to a number of littlein the podium, which was a long open platform, or P asS j l6encompassing the edifice at an elevation of some feet fro 111area of the circus. The persons of the imperial family*..

admits

principal magistrates, and the pontiffs, only were » ( ^

into the podium. Behind the podium there was a lit"® .with a precinctum, in which small doors were distnThe seats rose one above another, their whole Height,manner of steps, and were supported on the inclined vathe gallery or portico beneath them, and ascended f roinpodium to the top of the external wall. . j re g,

The great circi, as well as the theatres and amphiu> e g [were divided into several ranges of seats, for the P r ul ‘ se ot9placing the spectators according to their condition. Th® ^ (e (began from the wall at the back of the podium, aD “ raI1 k,setting off a sufficient number for persons of the fi rst ,‘ t# othe staircase of seats was interrupted by the omission ®or three, which formed an ambulatory, or via, simila r . e9podium, at every certain number of seats. Separate stailed to each via, through doors in the precinctum; these r ^tures were called vomitoria. As the spectators enter ^ 0 u^these passages at the top of the ranges of seats, theyhave to descend to occupy the first rows of each m pg,and since the seats themselves were too high to serve a 9 j^tostaircases, called scalares, formed by cutting down a se g jtetwo steps, were provided. The scalares were placed t jjethe vomitoria, beginning from the via, and descending ^ e fglower seat of each range; by this means the rang e8 fiedivided into a number of compartments, called cunei, as t j,jstheatres and amphitheatres; in the latter they obtain ^ t j)ename from their radial direction, and though the sl ® e3 J) tly 0circus were straight, and the compartments consequ®a rectangular form, they were called cunei, from usag fieOver the seats was a portico, or covered gallery* ^ fitaccommodation of the lower class of people. The P i3the emperor was called pulvinar, the situation ot ]og’^not known: it is supposed to have been a magni *f> reTo render the seats more comfortable, they weie

with wood.

ii>ii n wu« ■cir«°!‘

The extremity of the circus, opposite to the sem ^ fi\rend, was called the oppidum, and consisted of a sen® 8teen arcades. The centre arch, of the same height, " ^ ee c 'lthan the rest, served as an entrance to the circus, „jit«extremity of the oppidum, was a tower, which sur gTC b^every other part of the edifice. This combination ei)®"and towers, seen at a distance, gave the idea of a cast ®> fiee^was derived the name of oppidum. To what p® r P r ein al11towers were appropriated, is not known. The twei'' ^eg 9 ^'ing arcades were the career®, whence the chariot-r eJjtr an®^These career® were placed six on each side of 4 an d e* e 8 twhich was intended for the use of the processions, ge gin ea ^disposed, by the inclination of the chord-line of t t jpgon which they may be said to be set off, that the_ 9 0 f tthe twelve chariots was equalized. The divisio^ 0et°'^ earcades within, on the front, were ornamented W1 .jgg; ^supporting a cornice, in the manner of ht *

career® were closed with grated doors, to the b S

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