The big cistern was placed near the palaces and it is estimated that it had a diameter of 4.55 m and a depth of 6.20 m. The cistern was enclosed with small ashlars (large square-cut stones, typically used as a facing on walls of brick or stone.) with different dimensions and between the ashlars and the cistern was a fill of quarried stones and lime mortar. The inner ace of the cistern was covered with ashlars covered by plaster. In the middle of the cistern was a round pillar and probably the ceiling was made with wooden beams. In case of a fire, two persons were removing the cover from the cistern and then, at least four human chains were taking the water from the cistern to the fire.