Why did Persia invent the first highways and courier service?

Persia invented the world's first highways (although previous civilisations prepared the infrastructure) and the first courier system that allowed messages from the king to the satraps to pass back and forth quickly. The roads facilitated military conquest and control of the empire and facilitated trade across the empire. This source-based homework task is designed to facilitate student understanding of the NSW Ancient History syllabus for the Australian Curriculum
Higher School Certificate course
Historical Periods
Option D: Persia - Cyrus II to the Death of Darius III