Sacsayhuamán

"The living rock was excavated for the foundation, which was prepared with such solidity that it will endure as long as the world itself. The work had, according to my estimate, a length of 330 paces, and a width of 200. Its walls were so strong that there is no artillery which could breach them.

The principal entrance was a thing worthy of contemplation, to see how well it was built, and how the walls were arranged so that one commanded the other. And in these walls, there were stones so large and mighty that it tired the judgment to conceive how they could have been conveyed and placed, and who could have had sufficient power to shape them, seeing that among these people there are so few tools.

Some of these stones are of a width of twelve feet and more than twenty long, others are thicker than a bullock. All the stones are laid and joined with such delicacy that a rial could not be put in between two of them."

- Pedro Cieza de León, Spanish Chronicler 1553

https://www.bing.com/images/search?q=Sacsayhuaman+walls