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HISTORY OF ENGINEERING.

Book I.

with a magnificent bridge, that- still remains entire, and has defied all the ravages of time ; itis an early instance of a skewed bridge, and was afterwards adapted to form the port of acanal or basin, for the convenience of the boats provided for the consular army, which marchedby the Emilian way to the provinces.

Pliny ’s correspondence with the emperor Trajan proves the importance attached to thissubject; the consul in a letter (50.) points out such designs as were worthy the gloriousand immortal name of Trajan , “ they being no less useful than magnificent.” He describes anextensive lake near the city of Nicomedia, upon which the commodities of the country wereeasily and cheaply transported to the high road, from thence were conveyed on carriages tothe sea-side at great charge and labour; to remedy this inconvenience, he recommends thata canal should be, if possible, cut from the lake to the sea, observing that one had alreadybeen attempted by one of the kings of the country, but whether for the purpose of drainingthe adjacent lands, or making a communication between the lake and the river, wasuncertain: these useful works, in common with all others, fell to decay with the declineof the Roman empire: during the disastrous period which succeeded, until the time ofCharlemagne , Europe is deficient in any examples of similar undertakings: this sovereigncommenced the projects of uniting the Rhine to the Danube , and of opening a new com-munication between the German Ocean and the Black Sea .

The Italian republics, in the twelfth century, revived the arts and sciences, and the firstsigns of returning activity was to open the navigation by sea and by rivers long neglected.The Venetians, driven by Attila from the neighbouring lands of Italy , assembled them-selves in the marshes of the Gulf of the Adriatic, which, in process of time, gave rise to anew maritime city, preserving a semblance in its laws to the ancient Roman republic ;they soon converted the marshes into ports of great security, and the waters were coveredwith numerous fleets, which enabled them to carry on a commerce with the east, by whichthey became the merchants of all Europe .

Between the twelfth and fifteenth centuries, various improvements were effected in thenavigation of the Brenta, from Padua to Venice ; the Mincio from Mantua to the Po; theArno from Pisa to the sea; the Reno from Bologna to Primaro; the Tesino and Adda toMilan: and on this latter occasion, the Italian architects adopted the use of movable gatesto sustain the falls of the river, and afford a passage to boats whether the level rose or fell;for this discovery in the improvement of internal navigation we are indebted to Italy .

Mantua , after the death of the Countess Matilda , became a republic, and one of its firstefforts was to improve the navigation of the Mincio, so celebrated by the poets.

Its waters then overran the country, and becoming stagnant, rendered all the air around itunwholesome; in its course towards the Po, it formed three arms, and discharged itself withso much rapidity, that it was useless for navigation. In 1188, Alberto Pitentino erected thatfamous structure of stone, resembling a bridge and portico, which unites the gate ofCepetto with the neighbourhood of the ports, the object of which was to form the upperlake by the drainage of the marshes; he converted the Mincio into a canal, and restored itto its ancient course, uniting it with the Po, from whence it had been diverted in the timeof the Romans by Quintus Curtius Hostilius; this great work consumed ten years in theexecution, and the rise and fall was regulated at Governolo, in such a manner that boatscould ascend to Mantua and descend to Po, and the depth of its waters was so equallymaintained, that it was navigable for a distance of twelve miles: it is from this period wemust date the application of locks.

The. Lake Maqgiore is the source of the Tesino, which in its course is divided intoseveral streams, but which are again united before it enters the Fo, near Pavia. For thewhole distance it is navigable, although at Pan Perduto, where the fall is considerable, it issometimes hazardous. Immediately below this spot commences the canal to Milan,which at Abbiatc divides into two channels. The entire length of the excavation is about32 Italian miles, and its breadth 70 Milanese cubits.

The Canal della Martesana, by some supposed to have been executed by Leonard! daVinci, was made in the year 1460, under the Duke Francis Sforza; Leonardi da Vincijoined the two canals some time during the reign of Francis I . The Canal della Marte-sana, which is drawn from the Adda, is in length 24 miles, and width about 18 cubits;but when constructed at first, the water it contained was barely sufficient for navigationfor more than two days in the week, and this, when all the openings for the purposes ofirrigation were closed.

One of the branches of this canal was carried for several miles by a stone dyke, andafterwards passed through a deep cutting; the other branch had its course through therock, after which it was supported on one side by a lofty embankment, where it crossed theMoigara river by an aqueduct of three stone arches.

Before the introduction of locks, contrivances called conches were in use to moderatethe too great declivity of the rivers, and which were opened to allow vessels to passthrough: these openings were 16 or 18 feet in width ; a balance lever, loaded at the end,was made to turn on a pivot, and with it three hanging posts, united by an iron bar,