1that 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.
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.
CHAP. VI.
Of Bridges both of Wood and Stone, their proper Situation, their Peers,
Arches, Angles, Feet, Key-ſtones, Cramps, Pavements, and Slopes.
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 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
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