What is difference between Viaduct and Bridge?

I'm afraid I disagree with the first two answers. What they call a viaduct was in fact an aquaduct (water carrier) by the Romans. You can gain some insight on that at the address below. In a nutshell:

1. A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle,

2. A viaduct is a bridge connecting two points of equal heights,

3. An aquaduct is a bridge whose sole purpose is to convey water on the other side of a physical obstacle.

Can't say I know more than that, sorry.

Merry Xmas

from Wikipedia:

A viaduct is a bridge composed of several small spans. The term viaduct is derived from the Latin via for road and ductus to conduct something. However the Ancient Romans did not use that term per se, it is a modern derivation from an analogy with aqueduct. Like the Roman aqueducts, many early viaducts comprised a series of arches of roughly equal length. Viaducts may span land or water.

Viaducts were first built by the Romans to carry water from the mountains to the cities. Bridges carry people and vehicles across rivers and gorges. There was a combination bridge and viaduct in Rochester NY that carried the Erie canal on one level and people on the other level.

well, strictly speaking the water carrying bridges are usually referred to as aqueducts, but never mind!

the viaducts main claim to fame are that the bridge supports are constructed in a series of arches much like the old ancient roman aqueducts were.

a viaduct is for transporting water and was made famous by the Romans. This is where the word comes from. Bridges are generally used for traffic and transporting cars trains people etc. There are, occaisonally, structures that transport both traffic and water. but this is rare. good luck

There s nothing under the viaduct,,,river road etc....But there can be a river or road under bridge....Am I right?