They are not typical of the local g

They are not typical of the local geology- indeed, the source of the bluestones, the first stones erected, has now been traced to the Preseli Mountains of south-west Wales. Somehow these enormous stones were transported to the Salisbury Plains. The stones were surely too heavy for timber rollers. Perhaps they were transported on sledges, on greased tracks of wood, pulled by rope that had been made from the plant fibre of the indigenous lime bark soaked in water for weeks. Modern engineering simulations have surmised that the massive uprights were hauled into place then tipped, using stone counterweights, into position, demonstrating an understanding of the centre of gravity.