Cusco was not the only building that showed signs of vitrification and incredibly accurate stonework. Up on the hill above the city rests Sachsaywaman, a massive fortress built from excessively large stone blocks. Some of the granite and anthracite weighed upward of 300 tons. Despite how difficult it must have been to move them into position, they to show evidence of extremely exact join work. The vitrification that occurs here seems to indicate that high heat was used to shape or connect the megaliths with very narrow seams between them. Some of the large stones have apparently molten scars from whatever process vitrified their surfaces long ago.