Underground as well as above ground pipes, arches, an accurate gradient, and inverted siphons are all important features of ancient Roman aqueducts. The aqueducts provided water for drinking as well as for fountains and bathing that later emptied into sewers. The Romans built most of their aqueducts underground with only 29 miles viewed above ground.
Underground pipes helped control the health of the city as germs could not get into the water supply. Also, during wartime, the aqueducts appeared hidden so that soldiers always had a ready supply of water. The rich also used these waterways to water their gardens.
The arches designated where the aqueducts were placed. They helped to keep the flow of water from flooding their sides. These appeared often over hilly terrain or land with holes. They showed the skill of the architect with their beauty. The gradient generally less than 1/4800 was such that clotting or overflowing of the aqueduct didn't occur. The Romans made them so that gravity alone powered the aqueduct.
Inverted siphons, like the arches, helped to keep the water flowing over rough terrain and into the water supply. The inverted siphons moved water uphill as well as over lower-lying parts of the earth. They laid the closed pipe across the valley floor. Air shafts forced the water to flow into the pipe and let the water flow freely over rivers or other large depressions.
Vitruvius recommended masonry channels and clay pipes as building materials for aqueducts. These do not contain toxins like lead. Eleven Roman examples are the newer Aqua Claudia and Aqua Anio Novus, and the oldest waterway, Aqua Appia, built around 312 A.D. Others include Marcia, Tepula, Julia, Virgo, Alsientina, Traiana and Alexandrina. Roman architects built the earliest aqueducts from cut-stone. Remains of many of the arches stand today: Porta Furba, Tor Fiscale, Roma Vecchia, and Valle degli Arci.
The Romans chose the source of the aqueduct carefully as it had to last a long time. Other features included the length and width of the pipeline. Over 300 miles of aqueducts exist. Some channels considered short in length had many branches that fed many cities around Rome. For instance, Aqua Marcia was only 56 miles long but supplied the best water and was the first high-level channel.
Many of the aqueducts covered the same area. The Romans built them adjacent to one another. Evidence shows that Aqua Julia rode on top of Aqua Tepula which rode above Marcia. This practice shows that the Romans didn't waste energy looking for new sources of the water. They just built the channels near the ready-made ones leaving examples for others to follow.