Of all the urbanized people of the Americas, the Incas were the most brilliant engineers. The Incas built massive forts with stone slabs so perfectly cut that they didn't require mortar - and they're still standing today in near-perfect condition. They built road networks through the mountains from Ecuador to Chile with tunnels and bridges. They also built aqueducts to their cities as the Romans had. And of all ancient peoples, they were the most advanced in medicine and surgery.
The essence of Inca architecture cannot be distilled into a single word. Three themes demand recognition: precision, functionality, and austerity. The Inca stone-fitters worked stone with a precision unparalleled in human history; their architects clearly esteemed functionality above decoration; yet their constructions achieved breathtaking beauty through austerity of line and juxtaposition of masses. The Inca seem to have presaged Mies Van der Rohe's philosophy of "less is more".
Today's famous tourist destination "Macchu Picchu" is the last stronghold of the Inca Civilization.