men moved everywhere : operating the little railway bringing the huge stones , the smallest of which weighed two tons and the largest as much as ten , from a specially opened quarry about a mile away ; driving the steam cranes which lifted the heavy pieces of masonry into place ; laying the mortar which would hold them firm ; unloading pieces of steel , cement , tools and all the other equipment which had to be brought by horse and cart from the railhead at llanfyllin ten miles away ; making the new road that would encircle the lake when it was filled , and building that strange tower at the side of the valley , a few hundred yards north of the dam .