MEANS OF COMMUNICATION. 37 
eut stone and built upon deep-laid foundations, the river having been turned 
from its bed for the purpose. The stones were bound together with iron 
clamps set with melted lead. The starlings formed an acute angle; down- 
stream the pillars were semicircular; the roadway was 380 ft. wide and 
consisted of cedar and cypress timbers overlaid with palm wood. <A draw- 
bridge was raised every night to break the communication. Without doubt 
all the bridges of antiquity differed but little in their construction from this. 
The Romans are the first the remains of whose bridges have come down 
to the present time. So great was the importance which they attached to 
these structures that the supervision of them was intrusted to a priest who 
received his title therefrom, Pontrrex Maximcvs. 
Before we enter upon the details of the subject we will lay down certain 
well established principles respecting the position and construction of 
bridges, which principles must rest upon the four conditions which should 
govern all architectural structures: suitableness or convenience, durability, 
beauty, and economy. 
The situation of the bridge should be such at the confluence of streets or 
highways as to shorten the journeys of the greatest number of individuals 
without uselessly increasing the number of bridges. The bridge should be 
located upon a good foundation, and where it is in no danger of being 
undermined by the water. 
The direction of the bridge should correspond with that of the streets 
leading to it, or nearly so, that the entrance of vehicles may be unobstructed 
and easy; and its axis should be perpendicular to the direction of the 
stream, that the bridge may be as short as possible and the piers present 
their shortest face to the current. 
There should not be any considerable ascent or descent from the street 
to the bridge, while at the same time the bridge must be so high as not to 
_ obstruct the water-way. 
The width should be such that vehicles may pass each other, while upon 
each side there must be sufficient room for foot passengers, except in bridges 
of short span where there is but little travel ; in such cases, if two carriages 
chance to meet at opposite ends of the bridge, one of them may wait, and 
the roadway may be sufficiently wide only to accommodate one at a time. 
The foundations must be well laid and broad, particularly where the 
ground beneath is not solid, and in such cases they may be carried up in 
steps, as seen in pl. 7, fig. 14a. 
The form of the bridge must be decided with relation to the material 
employed and other attendant circumstances, whilst its beauty will result 
from the proper application of architectural principles. 
There are three distinctly different constructions of bridges, according as 
they are built of stone, wood, or iron. 
A. Stone Bridges. 
We turn now to the construction of stone bridges, which, from the rudest 
form of rustic bridge seen in pl. 7, fig. 1, to the noble structure represented 
in jig. 23, are characterized by a feature common in some shape to them all, 
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