Limestone and mud-brick were the main building materials used at Persepolis. After natural rock had been leveled on the plain, and the depressions filled in, tunnels for sewage were dug underground through the rock and the platform began to rise. A large elevated cistern was carved at the eastern foot of the mountain behind the platform to catch rainwater for drinking and bathing. The complex was partly cut out of the Mountain Kuh-e Rahmet ("the Mountain of Mercy"). To create the level terrace, large depressions were filled with soil and heavy rocks which were then fastened together with metal clips; upon this ground the first palace at Persepolis slowly grew.
