Chap. IV.

ROMAN.

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1345, after the designs of Taddeo Gaddi ; it has three arches the segments of circles,from 94 feet 6 inches to 85 feet span; and from 15 feet to 12 feet 10 inches rise. Thethickness of the key-stone is 3 feet 3 inches, the springing line of the arches is 11 feet5 inches above the level of low water. The thickness of the piers is 20 feet 4 inches, andthe breadth of the bridge 105 feet. It is built on piles, and a general framework ;on the upper side of the bridge is a covered gallery constructed by the Medici , andforming the continuation of a passage from the Pitti palace to that of the old Ducal.Under this gallery, on the middle of the bridge, are left open three arcades ; the goldsmiths’shops occupy the sides. The bridge of the Goldsmiths is one of the first modern bridgeswhere a segment was employed ; its springing is near the level of high water.

Bridge of the Carraja at Florence, rebuilt by Taddeo Gaddi , consists of five arches,which are segments, 57 feet 5 inches to 88 feet span; the versed sines are 12 feet 5 inchesand 26 feet 10 inches; it is built on piles. The facing walls are of squared stone, the rest,as well as the arches, are in moellon.

Bridge of Alcxandrie on the Tenaro, was built anterior to the year 1487, when four ofits arches were taken out, and reconstructed. It has ten arches, segments of circles,from 52 feet 5 inches to 95 feet 2 inches span. The upper part forms a covered gal-lery, 24 feet wide, the roof of which is supported by small arches, 7 feet 8 inches span ;during the time Piedmont was occupied by the French , they constructed a general platformunderneath this bridge, to form a movable sluice, by which they could fill the ditches ofthe citadel in case of siege.

Ponte Felice, over the Tiber at Rome, was built in 1587, under Sixtus V. , by DominicaFontana; it is composed of four arches; the two outer are 38 feet 9 inches, and thetwo middle 51 feet 2 inches span, nearly semicircular, and supported by piers 24 feet 7inches thick. Over the arches arc sculptured bas-reliefs.

Bridge over the Amo at Pisa , called the middle, was constructed after those at Flo-rence, in 1660, by Francis Nave. It is composed of three segmental arches, from 68 feetto 73 feet 7 inches span, and from 12 feet 2 inches to 14 feet 2 inches in height. Thepiers are 19 feet 3 inches in thickness ; the outer work is marble, and the rest brick ; theleft pier is surrounded by a starling, which serves to strengthen the foundations.

Bridge on the Rialto at Venice was built in 1578 by Michael Angelo, and has a singlearch 96 feet 10 inches span, and 20 feet 7 inches high. The footways are supported bycorbels provided with ballusters ; on the two sides are rows of shops, formed by marblearcades ; the interval which separates them constitutes three passages, the middle beingthe largest; this bridge is not intended for carriages. The approaches are steep, aidedby marble steps.

Bridge at Vicenza resembles the Rialto ; the slope is still more steep, and is only usedby foot passengers ; it has a single arch 101 feet 4 inches span, and 30 feet high.

Ponte Corvo near Aquino, over the Melza ; in the fourteenth century, it was in vainattempted to construct a bridge in this situation ; the bad quality of the foundation and therapidity of the torrent rendered all the efforts of the kings of Naples useless. Stephanodel Piombino at last proposed to construct one on a circular plan, whose convexity shouldbe opposed to the action of the current, and this idea was adopted, it being considered thatsuch a form would ensure solidity. This bridge was raised on a timber framework, whosesurface lay 6 feet 6 inches below the mean level of the water. The piers are formed oflarge blocks of stone, securely cramped, and defended by several rows of piles, their basehas four courses of stone, from 13 feet to 16 feet 5 inches long, also cramped, and presentinglarge sets-ofF; as has been observed, the foundations have a circular plan, whose radius is577 feet 6 inches. The arches are seven in number ; they are from 74 feet 5 inches to 93feet 10 inches span ; the thickness of the piers varies from 10 feet 8 inches to 12 feet 9 inches ;the breadth of the bridge is 42 feet 7 inches. The torrent being dry for a considerable partof the year, the foundations were laid in one campaign ; a great number of workmen aswell as soldiers were employed; the following year they raised the piers above themean level; Stephano died before the completion, and was succeeded by his son, Au-gustino, aided by Joconde of Verona, who was afterwards called to Paris to construct thebridge of Notre Dame; it was finished in 1505. Its solidity is not increased by thecircular form given to its plan, but by the construction of the frame-work, which wouldequally have resisted the action of the current had it been in a right line; if some wearingaway had occurred, it would only have been partial, and it is impossible that the bridgecould have been carried away in one piece, which might happen to a dam 30 or 40 feetlong : the disposition adopted has the inconvenience of obliging the piers to be inclinedtowards the current, which presents more resistance to the stream, and consequently injuresthe solidity of the bridge.

Bridge of the Trinity at Florence was constructed in 1750 by Ammanati , a celebratedarchitect . This bold work consists of three arches, nearly elliptical, the curve beingportions of two parabolic arches, whose angle at the top is masked by an escutcheon. Thespan of the arches is from 87 feet 7 inches to 95 feet 10 inches ; the springings are 7 feet