The Persian Empire had grown. Grown beyond the bounds that it had been born into. Like a baby out of a cradle, it had learned to walk.
But now, Persia had grown too large to walk. The army would expand the borders faster than people would reach them. Often, the only places one could get news from was wherever the armies were campaigning.
Clearly, something needed to change.
Zaraxes, Emperor of Persia throughout these times of growth and advancement, had a plan.
The Great East-West road wound through his lands, but they only connected a thin strip of cities in Persia. These cities flourished in the conditions, but the promising lands away from the road were pathetically underdeveloped.
"What" thought Zaraxes, "If Persia were to build roads throughout all of its lands?"
The possibilities came to him instantly. More agriculture. More population. A more easily-defended nation.
With the increased agriculture and population that would be brought on by the opening up of the unpopulated but arable regions of Persia, a larger army could be supported. This would start the cycle of expansion. More land could be taken, infrastructure and agriculture quickly built up, then the nation could expand further.
So thus did the Imperial Road System come into existence. One major stepping stone in Zaraxes' dream. The dream of the glorious Persian Empire of the future.