bridges are made to cross the rivers by train.
It's better than swimming across.
Steel
Favorite materials for bridges include steel, aluminum, titanium, wood, stone, and reinforced concrete.
Gold is rare, Gold is heavy, Gold is soft.
Arch bridges are made from arches. Arches are typically made from brick, reinforced concrete, stone or steel. Wooden arches are sometimes used for ornamental bridges, such as decorative footbridges in gardens.
The primary building materials in cable-stayed bridges are steel, which is used in the cables and also as the reinforcing material in the concrete, which is the other primary building material.
steel bridges are made out of steel OBVIOUSLY !!!
Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.Ancient Roman bridges were made for the same reason we make bridges today---to cross a river or any other geographical feature more easily.
by hand
An innumerable number of snow bridges hide deep crevasses, otherwise, there are no man-made bridges on the continent -- nor are there any roads.
iron and steel
'Tarred bridges' presumably means what it says: bridges that have been coated with tar. This presupposes that the bridges are made of wood, and the tar has been applied as a preservative and waterproofing treatment.
We can reasonably infer that the first bridges were logs, thrown across narrow streams.
By Technology developing and also people researching how to make bridges and thinking of new ways to make bridges and new materials to use.
Truss Bridges=Trusses have been used extensively in bridges since the early 19th Century. Early truss bridges were made of wood.==in additon the classic American covered bridges are all trusses, though the wooden truss members are covered by walls and a roof, for protection from the elements. Later truss bridges were made of cast iron and wrought iron. Most modern trusses are made of structural steel.=
The first bridges are likely to have been fallen trees or logs placed across streams.
Steel
the strengths of a arch bridges is that it is made in a shape that holds up more and for boats to go under