What do the red lines on the map below represent?

The red lines on the map below represents the Trans-Saharan trade route

Explanation:

The Trans-Saharan trade route is the route of trade that involves the transfer of goods such as live stock, pottery pastoralism, and the establishment of settlements between sub-Saharan Africa and North Africa, across the Sahara.

Trading in the Trans-Saharan trade route peaked between the 8th and the 17th century. The nature of the environment of the Sahara, through which the trade flourished was one an area where pastoralism existed which was around several thousand years BC

is there a year set? the question is incomplete