Archimedes Texts

76
that the Buildings there did not joyn one to
ano her. Plato, on the contrary, is so far from
approving of those Separations, that he would
have the Houses all close contiguous, and
that the joyning together of their Walls should
make a Wall to the City.

Of Bridges both of Wood and Stone, their proper Situation, their Peers,
Arches, Angles, Feet, Key-stones, Cramps, Pavements, and Slopes.

The Bridge, no doubt, is a main Part
of the Street; nor is every Part of the
City proper for a Bridge; for besides that it
is inconvenient to place it in a remote Corner
of the Town, where it can be of Use but to
few, and that it ought to be in the very Heart
of the City, to lie at hand for every body; it
ought certainly to be contrived in a Place
where it may easily be erected, and without
too great an Expence, and where it is likely
to be the most durable. We should therefore
chuse a Ford where the Water is not too deep;
where the Shore is not too steep; which is
not uncertain and moveable, but constant
and lasting. We should avoid all Whirl
pools, Eddies, Gulphs, and the like Inconve
niences common in bad Rivers. We should
also most carefully avoid all Elbows, where the
Water takes a Turn; for very many Reasons;
the Banks in such Places being very liable to
be broken, as we see by Experience, and be
cause Pieces of Timber, Trunks of Trees, and
the like, brought down from the Country by
Storms and Floods, cannot swim down such
Elbows in a strait Line, but turn aslant, meet
and hinder one another, and lodging against
the Piles grow into a great Heap, which stops
up the Arches, and with the additional
Weight of the Water at length quite breaks
them down.

OF Bridges, some are of Stone, others of
Wood. We shall speak first of those which
are of Wood, as the most easy of Execution;
next we shall treat of those which are built of
Stone. Both ought to be as strong as possible;
that therefore which is built of Wood, must
be fortified with a good Quantity of the

strongest Timbers. We cannot give a better
Example of this Sort of Bridges than that built
by fulius Cæsar, which he gives us a Descrip
tion of himself, as follows: He fastened to
gether two Timbers, leaving a Distance be
tween them of two Foot; their Length was
proportioned to the Depth of the River, and
they were a Foot and an half thick, and cut
sharp at the Ends. These he let down into
the River with Cranes, and drove them well in
with a Sort of Rammers, not perpendicularly
down like Piles, but slanting upwards, and
giving Way according to the Current of the
River. Then, opposite to these, he drove in
two others, fastened together in the same Man
ner, with a Distance between them at Bottom
of forty Foot, slanting contrary to the Force
and Current of the Stream. When these were
thus fixed, he laid across from one to the other,
Beams of the Thickness of two Foot, which
was the Distance left between the Timbers
drove down; and fastened these Beams at the
End, each with two Braces, which being
bound round and fastened of opposite Sides,
the Strength of the whole Work was so great
and of such a Nature, that the greatcr the
Force of Water was which bore against it,
the closer and firmer the Beams united. Over
these other Beams were laid across and fastened
to them, and a Floor, as we may call it, made
over them with Poles and Hurdles. At the
same Time, in the lower Part of the River,
below the Bridge, other Timbers, or sloping
Piles, were driven down, which being fastened
to the rest of the Structure, should be a Kind
of Buttress to resist the Force of the Stream;
and other Piles were also driven in at a small
Distance above the Bridge, and standing some
what above the Water, that if the Enemy
should send Trunks of Trees, or Vessels, down
the Stream, in order to break the Bridge, those
Piles might receive and intercept their Vio
lence, and prevent their doing any Prejudice
to the Work. All this we learn from Cæsar.
Nor is it foreign to our Purpose to take Notice
of what is practiced at Verona, where they
pave their wooden Bridges with Bars of Iron,
especially where the Wheels of Carts and Wag
gons are to pass. It remains now that we