Byzantine Spies and Espionage

By Georgios Theotokis

In human history there have been several unconventional methods of acquiring intelligence through espionage, an activity that was usually, but not necessarily, state-sponsored and which took place in times that preceded hostilities between states – the declaration of war being the key moment when we can draw a distinction between espionage and reconnaissance. Here, I will deal with the methods and dangers of information and intelligence flow that authorities in Byzantium could gather in local markets and fairs, important ports, and taverns and inns, and how they reacted to spies and espionage activity in these particular places.

It was not just regular movement and travelling that turned merchants into a natural source of information; it was also the places where they did business, where they socialised ‘after hours’, and the people they met there. Ports, markets and religious festivals were ideal places for intelligence gathering, since it was in such places that the most diverse individuals would converge during the day – this was a place of work but also a place of socialising with others, not just locals but international tradesmen of various religions and nationalities. The language barrier would not have been an issue in such hubs, as most of these men would have been proficient in Greek, Armenian and/or Arabic, and their frequent travels would have accustomed them to the given local traditions and way of life.


At ports, markets and festivals there would have been more or less unrestricted gossip about the political situation of the day, and rumours were passed on with surprising speed. Since antiquity, we can detect in military treatises a serious concern not over the members of the merchant class themselves, for whom distrust was mitigated since they were identified as non-combatants (άμαχοι, amachoi), but rather over spies infiltrating their ranks and posing as έμποροι (merchants). In AD 365, fearing for his life, Procopius avoided detection during his travels from Chalcedon to Constantinople, where he hoped to gather intelligence and hear the rumours circulating in the capital, due to his neglected personal hygiene and old clothes. The sixth-century treatise On Strategy similarly advises the following to all spies assigned on a mission:

‘Before leaving each spy should speak in secrecy about his mission to one of his closest associates. Both should agree upon arrangements for communicating safely with one another, setting a definite place and manner of meeting. The place could be the public market in which many of our people, as well as foreigners, gather. The manner could be on the pretext of trading. In this way, they should be able to escape the notice of the enemy.’


Both the Byzantines and the Muslims sought to reduce and impose strict controls over all commercial activity in the eastern Mediterranean after the initial Muslim conquests, for fear of espionage. An anecdotal narrative by al-Baghdadi (1002–71) in his Taʾrikh Baghdad (‘History of Baghdad’) relates how the Muslim attitude about city building was influenced by Constantinople, and the degree to which the Abbasids perceived the city as a model for imitation. In an alleged conversation between Caliph al-Mansur (754–75) and the ambassador sent by Emperor Constantine V (741–75), regarding the building of Baghdad:

‘The Caliph asked Patrikios, ‘What do you think of this city?’ He answered, ‘I found it perfect but for one shortcoming.’ ‘What is that?’ asked the Caliph. He answered, ‘Unknown to you, your enemies can penetrate the city anytime they wish. Furthermore, you are unable to conceal vital information about yourself from being spread to various regions.’ ‘How?’ asked the Caliph. ‘The markets are in the city,’ said Patrikios. ‘As no one can be denied access to them, the enemy can enter under the guise of someone who wishes to carry on trade. And the merchants, in turn, can travel everywhere passing on information about you.’

Naval espionage and the opportunity to obtain intelligence at major port-cities in the Mediterranean were also exploited by both the Byzantine and the Abbasid empires. In his Kitab surat al-ard (written c. 988), Ibn Hawqal complains that Byzantine merchants gathered intelligence while conducting their business at Muslim ports:

‘They [Byzantines] sent their boats on the territory of Islam to engage in trade, while their agents roamed the country by taking the information secretly and by gathering information, after which they left.’


The jurist Abu Yusuf (d. 798), who served as chief judge (qadi al-qudat) during the reign of Harun al-Rashid, acknowledged the danger posed by merchants in transmitting information to the enemy. Arabic-speaking infiltrators were sent by the Byzantines to the Egyptian port of Damietta in the Nile Delta before the Byzantine raid of 853, while imperial agents (ακριβείς κατάσκοποι) – probably camouflaged as sailors or merchants – were also dispatched by the protospatharius Leo to Tarsus, Tripoli and Laodicea to investigate whether the Muslims were aware of the Byzantine preparations for a naval expedition against Crete in 911.

The late eleventh-century Italo-Norman chronicler Geoffrey Malaterra reports that the Normans sent Philip, son of Gregory the patrikios, to Muslim Syracuse to gather information about the enemy’s army and fleet. He and his comrades were disguised as merchants and could roam around the port without attracting any unnecessary attention, ‘for both he and all the sailors who were with him were most fluent in their language [Arabic] as well as Greek’.

Finally, Kekaumenus provides a vivid description of the cunning methods used to gain access to the Thessalian port-city of Demetriada, stressing the fact that ships coming to trade should not be trusted at any time, as they might pretend to come peacefully: ‘We did not come here to fight [a war], rather to pay tolls and sell prisoners and other things we have from corsair activity.’ But, in reality: ‘the Hagarene . . . after climbing over the side of the walls, from where the locals had no suspicion, they climbed on top of the castle’s battlements . . . and they occupied the fortified city that was full of every goods immediately and without a battle.’

Medieval depiction of a market

Spies used obscurity as their camouflage to avoid drawing attention from the local authorities. Much of the evidence about spies in ancient Greece comes from the precautions recommended by the 4th century BC Aeneas Tacticus to be taken following the outbreak of war or during the siege of a city. According to Aeneas, in order to prevent any information from being passed on to foreigners or enemy agents posing as merchants, no festivals are to be held outside of the city and no private gatherings are to be allowed during day or night. Furthermore, ‘no citizen or resident alien shall take passage on a ship without a passport [σύμβολο], and orders shall be given that ships shall anchor near designated gates’. In order to enable local authorities to distinguish among friendly troops, agents or citizens from foreign lands and enemy infiltrators, several cities in ancient Greece had devised a series of verbal and written signs or signals called synthemata (συνθήματα), a common password that could easily be remembered (e.g. ‘Athena’ or ‘Hermes Dolios’) and tokens (σύμβολα) or sphragides (σφραγίδες, Lat. bulla).

The tenth-century Επαρχικόν Βιβλίον (Eparchikon Vivlion, The Book of the Eparch) by Leo VI, written probably around the year of his death in 912, also places strict restrictions and regulations upon the guild life and mercantile activity in the empire’s main cities and ports; for example, merchants coming from the Muslim world could not stay in the empire for more than three months. Security considerations also prompted the imposition of a ban on the export of weapons and any other material related to warfare – this ban was extended by Tzimiskes in 971 to include several kinds of timber. Qudama’s short naval guide advises the city and port authorities to be vigilant for the possible infiltration by spies – the fear of spies in Egyptian ports was greatly intensified after the raid in Damietta – and conduct thorough searches of every merchant leaving a Muslim port or city for any war supplies. According to Leo VI’s sixty-third Novella, the person who ignored the ban on the export of weapons would have been punished by death.

An ideal place to gather all kinds of intelligence about the enemy were the πανδοχεία or funduqs. These served as hostelry for travellers, but the institution took on new economic and social roles as, aside from catering to merchants’ lodging needs and providing storage for their trade goods, they functioned as places of sales and governmental taxation. As predecessors of modern hostels and inns, they were mainly situated alongside important roads, crossings and passes, and were places where anyone could meet and socialise with all sorts of people, including merchants and travellers who ate, drank and spent the night there. Here, one could recruit mercenaries, question witnesses, discuss contracts, conduct political negotiations and trade news and rumours – in a sense, these were the focal points of a town or a city where important and everyday people alike could meet after sunset and into the late hours. The important thing to bear in mind about these places is the diversity of people, trades, social and ethnic groups, and religions one could come across. Naturally, as these people would, usually, have consumed copious amounts of wine and/or ale, ‘their tongues would have gotten loose’.

Aeneas Tacticus also makes special mention of the innkeepers. During a siege or emergency situation, ‘even they’ should not be allowed to receive any strangers without permission from the city authorities. I have not come across any evidence in Byzantine primary sources regarding an incident involving people at a tavern, intoxicated or not, giving out secrets to enemy spies or agents, but we know, for example, from letters sent by Strasbourg spies from Breisach to their home town in 1417 that the city council had attempted not only to establish contact with the tavern-keepers, but even to send spies directly to them to catch up on whatever intelligence they could. Perhaps the most famous incident of revealing top-secret military information comes from 1944. On the eve of the Normandy landings, a drunken American, Major-General Henry Jervis Friese, publicly took bets at a London hotel that the D-Day invasion would occur before 15 June. This was in spite of the real threat of Nazi agents operating in London pubs, bars and hotels where Allied troops lived and socialised.


Ports, markets and religious festivals have been ideal places for espionage for millennia, since it was in places like these that diverse people mingled and conducted their business. There are many examples in our primary sources where the opportunity to obtain intelligence at major port-cities in the Mediterranean was exploited by both the Byzantine empire and its Muslim enemies. All military authors of the period are highly concerned with the activities of the έμποροι and with the spies that would infiltrate their ranks to collect intelligence. Therefore, in order to curtail the flow of information across the borders, central authorities resorted to placing severe restrictions on the activities of merchants, with mixed results for the effectiveness of blocking intelligence from reaching enemy agents.

Georgios Theotokis: Ph.D History (2010, University of Glasgow), specializes in the military history of eastern Mediterranean in Late Antiquity and the Middle Ages. He has published numerous articles and books on the history of conflict and warfare in Europe and the Mediterranean in the Medieval and early Modern periods. His latest book is Twenty Battles That Shaped Medieval Europe. He has taught in Turkish and Greek Universities; he is currently a postdoctoral researcher at the Byzantine Studies Research Centre, Bosphorus University, Istanbul. 

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