Final answer:
The middle division of the historical divisions of the Roman Empire is known as the High/Middle Empire, characterized by peace and prosperity during the Pax Romana period.
Step-by-step explanation:
The middle division of the three historical divisions of the Roman Empire is known as the High/Middle Empire. During the approximately 100 years between the reign of Trajan and the assassination of the last Antonine emperor, Commodus (98-192 CE), the Roman Empire reached its greatest geographical extent and experienced the continued peace and prosperity of the Pax Romana. This era, also called the High Empire, was marked by ongoing fighting at its borders but also by significant peace and prosperity within.