The masterfully engineered qanāt system was later adopted and developed by the Romans, who became the greatest aqueduct builders of the ancient world. To maintain the water’s gradual descent through high mountains, Roman engineers understood the importance of digging correctly angled ditches and tunnels, running from the high plateaus. When the pipelines reach the low valleys, the water is carried on elevated stone walls. If the aqueduct needs to be higher than six metres, the Romans saved building materials by arching the wall at regular intervals, using an ancient engineering technique. The arch revolutionised building technologies throughout the ancient world by allowing the construction of far greater spans along a single superstructure. This changed the spatial design of architecture. And in terms of strength and efficiency, the arch increased the endurance of large public and civic buildings. Hence, Roman aqueducts were able to withstand the powerful energy of water forcing its way from its source up in the mountains, down below to the valleys. And when the canal reached its destination, the aqueduct emptied its load onto three holding tanks: one for the public drinking fountains, another for public baths, and the third reserved for the emperor and the noble households. This was because the wealthy Romans had to meet the cost of their own running water. Nevertheless, and despite the efficiency of the aqueducts, the excess water in Roman cities was never stored. Instead, it was used to flush out the city’s sewers.