If nothing else, the Roman Empire had a good run. From Octavian’s victory at Actium (31 BC) to the date traditionally assigned to the empire’s demise in 476, it lasted a solid 500 years – an impressive number by any standard. In fact, the decline and final collapse of the Roman Empire took longer than most other empires even existed. Any historian trying to unearth the grand strategy of the empire must, therefore, always remain cognizant of the fact that he or she is dealing with a period that covers nearly a fifth of recorded history.

Although the pace of change in the Roman era never approached that of the past 500 years, Rome was not an empire in stasis. While the visible trappings may have changed little, there were vast differences between the empire of Augustus and those of his successors. Over the centuries, the empire’s underlying economy, political arrangements, military affairs, and, most importantly, the external challenges the empire faced were constantly changing. In truth, all of the factors that influence grand strategy were in a continuous state of flux, making adaptation as important to Roman strategists as to those of the modern era.