The Roman aqueduct system is one of the most fascinating aspects of ancient Rome (in my opinion, of course). Not only did these create important infrastructures for city development, but they also projected the power of Roman authority well outside the walls of cities.
Oh, and they were terribly ambitious as well!
Using aqueducts, the Romans were able to transport water dozens of miles from its source to cities and towns where it was accessible to the masses. The general idea behind this system was gravity; using a sloped surface, water would flow downhill (ever-so-slightly) from Point A to Point B. One of the problems with this system was that at times the aqueduct would need to run across valleys, which meant the flow of water had to occasionally travel uphill. The Romans tackled this problem by using siphons: ducts that hugged the ground received the water that ran down one hill, and this caused enough pressure to push the water in front of it up the hill on the far side of the valley.
In smaller valleys, the Romans had the option of building large, arched aqueducts in lieu of using siphons. The simpler post-and-lintel system could have been used to create these, but they would have required many more vertical supports than needed by the more practical arch (the Romans, of course, are known for exploiting the arch in their architecture). The arches were constructed using wooden scaffolding called “centering”.
These structures, which allowed the water to flow downward at a constant slope, had an effect which may have been equal to that of their practical use: they fostered the idea of Roman authority and might in lands far outside Rome itself. Imagine being a non-Roman who wandered into southern France circa 10 B.C. and seeing the magnificent Pont du Gard (see photo) straddling the river. Not only are the blocks of stone that make up the arches and piers massive in size, but there are three tiers of arcades which stretch a vast distance between hills. How would you have reacted?
For those who had never been to Rome (or any major Roman city), these kinds of structures would have astounded. What kind of civilization could create such works? What kind of power did they possess? The visual fireworks put on permanent display by these aqueducts would have impressed all who saw them for the first time. Thus, their utility was matched by their symbolic importance in helping to elevate the Roman Empire to heights that may have been previously unknown in the ancient world.
For more in-depth background information on aqueducts, see the site of W.D. Schram.