What Is the Distance Between Patna and Gandhar?

Let's say let's talk about 2000 years ago during the Kushan times. How did kings and administrators get updates as to what was happening in far off distant parts of their empire kingdom? So here we have India. Now let's take the example of Emperor Ashok for instance, he was one of our greatest emperors. He when he was a prince, not yet the emperor, he was the governor of Gandhar. His father obviously was in Patleputra which is present day Patna. Let us see from here to Kabul? That's 1,820 kilometers in a straight line as the crow flies.