Roman cities were prime examples of early engineering prowess. Especially when the Roman engineers built new cities from scratch; they were highly evolved, orderly, planned metropolises able to support tens of thousands of people comfortably. Pompeii had been under Roman rule for more than a century when it was buried under volcanic ash in 79 ce. The ash preserved the city like a time capsule and lets us see how Romans lived 2,000 years ago in their engineered cities. The water and sewer systems were important elements of a Roman city. Water came in via free-flowing aqueducts. It was distributed to citizens through pipes and public fountains. Excess water, human waste, and storm water flowed into a belowground sewer system. Roads were extremely important for letting people, animals, and carts move around the city. The city streets were paved with stones and laid out in a grid pattern much like they are in a modern city. Sidewalks lined the streets and were covered to shade pedestrians. The public baths were important both for hygiene and socializing. Many incorporated an ingenious heating system called a hypocaust. The floor of the bath was raised up on tile pillars with a 3-foot (1 meter) gap underneath. Smoke and heat from a fire would flow under the floor and through the walls to heat the bath to temperatures as high as 120°F (49°C). A Roman city also contained shops, workshops, bakeries, markets, a forum with its public temples and government offices, an amphitheater, and a performing theater. The citizens of the city lived in private homes or apartments. The building materials available to the engineers were stone, concrete, brick, tile, and wood. The Pompeii amphitheater, for example, is the oldest stone amphitheater in the Roman Empire. A typical home's walls were covered with plaster on the inside and often painted, with stucco on the exterior. Roof trusses were used, covered in roofing tiles. Engineers had created the height of urban luxury for the citizens of these Roman cities, delivering everything that large numbers of people needed to live comfortable lives.