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Military History

The Byzantine Empire: Medieval Successor to Ancient Rome

The Byzantine Empire, successor to ancient Rome, lasted over a thousand years. This was no thanks to Persia, Byzantium’s first major enemy and major rival.


by Arnold Blumberg

After the convulsions of the 3rd century AD, the old Roman Empire was divided among several rulers, with the senior emperors governing from the East. From the time of the Empire’s official split into separate western and eastern political entities in 395 AD, the latter region—the wealthier of the two—controlled the trade routes to Asia. It encompassed the granary of Egypt, the manpower of Anatolia and Thrace, and the great commercial cities of Antioch, Alexandria, and Athens. Its reach extended to the Crimea and stretched along the eastern coast of North Africa. All this was underpinned by its ancient Hellenistic culture and its assumption of the legacy of old, imperial Rome. By contrast, the Eternal City on the Tiber River became a mere provincial capital as western Europe fell into the grasp of barbarian Germanic tribes.

In the mid-6th century the eastern empire was able to reunite with the lands to the west. Under Emperor Justinian I(527-565) the Byzantines recovered Vandal-controlled North Africa, the Ostrogothic Kingdom in Italy, and part of Visigothic Spain. But this reconstruction of the old Roman Empire did not last long. The the people whose lands were acquired in the west no longer wished to be part of the Empire. The Byzantine Army could not hold the ground it had taken, and the government lacked the money to administer the newly conquered territory or pay its own army. Above all, an immediate threat from an enemy to the east raised great alarm and changed the Empire’s priorities.

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A great empire in ancient times until overthrown by Alexander the Great in the 330s BC, Persia revived in the 3rd century AD under the Sasanid Dynasty. From that time on, it served as rival-in-chief to the Byzantines. It would take all the skill—diplomatic and military—for the emperors at Constantinople to counter the growing Persian menace.

The Byzantine Empire’s Spy Network

The Byzantines would often resort to spying to thwart their enemy. They used both internal intelligence and spies beyond their borders. The Byzantine Empire inherited large administrative bureaus (officia), among which were departments used to giving notice of laws and regulations to the general populace. Agents of these departments also acted as spies for the government, sending back information on the intent and state of mind of the citizenry.


Such spies grew out of what were known in classical and Christian Rome as frumnentarii, or internal secret police, whose job was to keep an eye on domestic enemies of the Emperor. They could be loaned out as international spies when the need arose. Abandoned by Emperor Diocletian late in the 3rd century AD, the frumnentarii were more dispersed than suppressed, many of their functions given to other governmental agencies. Part of the frumnentarii organization passed to the scrinium barbarorum (an office of barbarian affairs) created by the Byzantines at the start of the 5th century.

Even in the very early years of the Eastern Empire the government relied on domestic spies to perform nondomestic spying. In the first part of the 4th century the senior Caesar, Constantius, developed a spy network that had the two-fold purpose of keeping his military in line and evaluating the potential of foreign military establishments. Using enlisted personnel and junior officers, the Emperor was able to control his ethnically diverse soldiery by disseminating among them favorable propaganda (favorable to the Emperor) and money to the ranks.

In addition, his agents would make contacts with members of the forces of other nations who had relatives serving in the Byzantine military. Cultivating these sources with false intelligence about the Empire’s army and intentions and handing out liberal bribes, operatives would glean valuable information about current and potential enemy plans and capabilities.

Internal spies could also act as a counter-intelligence resource. A system of government representatives served as imperial watchdogs for the administration. Appointed to key staff positions in the provinces, their main job was to curb corruption and abuse by local officials. But we know from their correspondence that they investigated more than just domestic problems in their assigned districts. They also supplemented the local governor’s reports with news of what was happening in neighboring countries, especially Persia. They reported the status of both foreign and friendly military movements and dispositions in times of peace and war to the Emperor. Further, they were urged to create local intelligence sources, and to counter attempts at intelligence gathering by current or potential foes of the Empire.

Estimates of the number of spies engaged by the Byzantine Empire to gain information about the Persians in the 4th through the 7th centuries range in the thousands. This period saw numerous battles fought, sieges undertaken, and many temporary truces brokered. The Byzantine employment of informants to gain background knowledge, strategic insight, and tactical intelligence to use against their opponent continued throughout this period of armed hostility and cold peace.

Prefects to the Byzantine Emperor

Byzantine praetorian prefects, such as foreign service, nevertheless represented the Emperor. They were high-ranking civilians or military men chosen by the Emperor to represent him and act as messengers to convey requests or demands to and from other governments. The whole arrangement was an ad hoc affair. As a matter of course, these envoys were recruited as spies, and the Persians knew it. Of course, Persian diplomats served the same purpose, and their Byzantine hosts would do all that was possible to prevent any valuable intelligence from reaching them.

Although treated with respect and accorded all the amenities, Byzantine foreign representatives had a hard time acquiring information. While in the Persian capital of Seleucia-Ctesiphon, they were quartered in an isolated area of the city and kept away from the local populace so that they could neither gather from nor give information to resident informants. All diplomats would be escorted wherever they went and were continuously under surveillance. The Byzantine mission of 579 went through what can only be described as a case of overkill by their Persian hosts. They were not allowed to travel at certain hours of the day or night, or on certain roads. They were forced to stop at way stations every few miles to slow their movements and thus limit any opportunities to see or hear anything the Persians did not want them to be aware of. Upon their arrival at the capital they were so closely watched that one of them recorded in exasperation that the guard assigned to the envoys did not allow them to breathe fresh air or even put their heads out of the buildings where they were lodged.

If emissaries of the Byzantine Empire had a difficult time spying for their country, the same was true of any Byzantine merchant attempting to conduct his business in Persia. The reason was simple: For centuries the favorite cover for a Byzantine spy trying to infiltrate Persian society was to disguise himself as a foreign trader. So whether the man was a real merchant simply trying to ply his true trade or a government spy posing as a merchant, all foreign sellers or purchasers were suspect. To regulate this activity the Persians (and Byzantines) required all merchants, foreign and domestic, to travel to and from trading centers by approved routes, and to conduct their trading activities only at a few specified centers or cities along the common border.

Originally Published April 27, 2014 

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