The Incas most famous achievement is sharing of new ideas from different cultures a large religious organization of missionaries the development of an extensive road system the development of a calendar system

The development of an extensive road system.

Explanation:

In order to keep their vast empire under control, the Incas needed good communication between the areas they ruled.

That is why they worked on building routes and managed to develop an impressive road system which facilitated trade as well as communication between the Incan municipalities. These roads were crucial in maintaining authority over newly conquered lands.