The majority of Roman aqueducts were built underground and at a modest downward inclination to enhance water flow. Siphons were used to transport water across a low basin or valley. When the aqueduct reached the other side, the siphon was broken and the water flowed freely into another channel or tank where it could be distributed through more conduits or dropped over the end wall of the tank into areas where it was needed. Aqueducts were one of the most important inventions of the ancient world and played an essential role in making possible the growth of large cities such as Rome. An aqueduct was typically made up of several channels or pipes connected together under pressure. It was usually buried in rock crevices or trenches dug in the ground. The deeper the channel, the faster the water would flow. Channels were often separated by small vertical spaces called "jogs" to reduce the amount of time it took for water to travel from one channel to the next. These days, engineers use a similar design concept when they build pipelines for drinking water supplies. In addition to being useful for supplying water, aqueducts provided cool, clean water that was ideal for drinking, cooking, and washing. They also helped control disease by reducing the concentration of pathogens in water sources that were likely to be contaminated with animal feces.