What is considered the greatest example of incan engineering?

The city of Machu Picchu is considered the greatest example of Incan engineering. Machu Picchu (also known as the Lost City of the Incas) is a city of stone built atop a high ridge in the Peruvian Andes around 500 years ago without the aid of wheels, iron or steel tools.  It possesses over 600 terraces which prevent the city from sliding down the mountain. These terraces retained and channeled moisture and preserved soil, and provided the necessary space for agriculture. To distribute water throughout the complex, a canal was constructed by Inca architects, and it supplies water throughout a length of over 1 km. These incredible engeneering feats have made Machu Picchu possible, and they have also protected the region from heavy rains and earthquakes.  The city of Machu Picchu is recognized as an architectural masterpiece.

The Inca or Incan Empire ruled between the early 1200s and 1572, a large chunk of pre-Columbian South America, from modern Ecuador to Chile. Cusco served as the administrative, political and military centre for the Empire.

Two of the best examples of Incan engineering are the iconic mountain citadel of Machu Picchu and the ancient capital of Cusco.

Some of their engineering standout achievements in engineering include:

In conclusion, the Incas were innovators and pioneers in many aspects of engineering, building some of the most marvelous and renowned structures by any civilization in harmonisation with the nature, and all of which was accomplished without the use of the wheel.

b) to encourage free trade