How was classical persia’s extensive network of roads important to its civilization?

The royal road built in Persia during the Achaemenid dynasty proves to be the greatest  achievement in improving the civilization of Persia.

Explanation

The royal road led from Aegan sea to Iran and it is around thousand five hundred miles. This road was built when the area was uninhabited by the people. But as soon as it was laid, many cities sprang up like Susa and Sardia. The roads from Susa to Persopolis which connected to India. Thees roads also interconnected canals from Nile to Red sea.

From the historic records, it was found that human porters can move up to ten to fifteen kilometers per day carrying loads of sixty to hundred kilograms.

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

answer; the period of time known as the middle ages;