Cusco Peru stone wall - Google Search. If you look closely, you will notice the precisely cut channel in the stone, which is designed to fit with another stone to make a complete link. Which is filled with molten copper to hold the two stones together, even in an Earthquake. But the question is, how was it cut? It is 'U' shaped at the bottom. But the channel goes into much tighter corners. We do not have that sort of technology today..