text:  The limestone used for construction was local and <unk> on @-@ site . The depressions formed by the extraction of stone for building were plastered to <unk> them and were used as reservoirs , together with some <unk> natural depressions . The main <unk> were surfaced with stucco and laid at a gradient that <unk> rainfall into a system of canals that fed the reservoirs . 
  