Wooden bridges of this
type appear on most of
our rural roads. This
one crosses T /i r k e y
Creek, on Lyda Road.
A steel bridge across
the Davidson River,
near the Ranger Station.
The world famous Golden Gate bridge across San Francisco Bay
has a 7,000 foot span.
cross narrow gorges or streams. Simple bridges,
consisting of logs or wood or stone, were used by
the earliest known groups of mankind.
The arched bridge was probably first used by
the Chinese. Simple brick arches have been dis
covered among Egyptian ruins, but it is unknown
if the Egyptians built arched bridges. Bridges are
not mentioned in the Bible, but according to other
records a brick arch was erected across the Eu
phrates river in the city of Babylon. Pontoon
bridges, which are carried on floating supports,
were used for military purposes by Cyrus and
other Persian kings as early as the 6th century
B. C.
The stone arch was developed by the Romans,
who used it especially for strong monumental
bridges, some of which are still standing. In the
l6th century, Leonardo da Vinci and Palladio in
vented the wooden truss and used it in construct
ing bridges. The first metal arch bridge was made
of cast iron and erected at Coalbrookdale, over the
Severn River in 1776—the river that caused Mar
garet of Anjou to lose her army to Edward, be
cause she could find no place to cross. Wrought
iron was used to replace cast iron after investiga
tions were carried out for Robert Stevenson when
planning the famous tubular bridge across Menai
Straight.
Later, steel displaced wrought iron, and ordi
nary steel has given way to special alloy steel.
The principal bridges that we see today are con
structed of wood, steel, concrete and masonry.
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