text:  The boulders were transported over 150 kilometres ( 93 mi ) from the source of the stone . The exact method of transportation of such large masses of rock are unknown , especially since the <unk> lacked <unk> of burden and functional wheels , and they were likely to have used water transport whenever possible . Coastal currents of the Gulf of Mexico and in river estuaries might have made the <unk> transport of monuments weighing 20 tons or more impractical . Two badly damaged <unk> sculptures depict rectangular stone blocks bound with ropes . A largely destroyed human figure rides upon each block , with their legs hanging over the side . These sculptures may well depict <unk> rulers overseeing the transport of the stone that would be fashioned into their monuments . When transport over land was necessary , the <unk> are likely to have used <unk> , ramps and roads to facilitate moving the heads . The regional terrain offers significant obstacles such as swamps and floodplains ; avoiding these would have necessitated crossing undulating hill country . The construction of temporary <unk> using the suitable and plentiful floodplain soils would have allowed a direct route across the floodplains to the San Lorenzo Plateau . Earth structures such as mounds , platforms and <unk> upon the plateau demonstrate that the <unk> possessed the necessary knowledge and could commit the resources to build large @-@ scale earthworks . 
  