The Roman Empire featured an infrastructure that allowed reliable communication between the emperors and all parts of the Roman administration, known as uehiculatio during the Principate and as cursus publicus from the late third and early fourth century CE onwards. This study aims, firstly, to explore the factors that led to the establishment of the cursus publicus with its two sub-divisions (cursus uelox, cursus clauulari(u)s); and, secondly, to show through a comprehensive review of the structure, history, and development of the cursus publicus in the fourth century that this system was firmly integrated into the imperial administration and sreamlined to such a degree that it could be used with unprecedented effectiveness by the end of the fourth century.