Byzantium and Venice: The Rise and Fall of a Medieval Alliance

By Georgios Theotokis

In the year 1081, the Norman Duke Robert Guiscard was preparing his most ambitious military expedition to date: to invade Byzantine Empire and fight his way to Constantinople. The Normans had already conquered the Byzantine outposts in Italy, and Guiscard knew that Byzantium did not have a naval force that could stop him from crossing the Adriatic Sea.

It was during this moment of crisis that the Byzantine Empire turned to their vassal and old ally, the maritime republic of Venice. The Venetians did not hesitate to send a large squadron to the Empire’s rescue, for they would be getting in return “some rewards that were pledged, others granted at once. All their desire would be satisfied and confirmed by chrysobulls, provided they were not in conflict with the interests of the Roman Empire.”


The story of the Venetian-Byzantine military alliance is a complex one, with many questions that need to be answered: What were the deeper political and economic reasons that pushed the maritime republic to send a powerful fleet in Adriatic waters? What were the Venetians hoping to achieve and what might had been their long-term objective? What evidence do we have from our chronicler sources about the naval battles that took place in 1081 and 1084 and how effective the presence of the Venetian fleet proved to be in defeating the Normans? What were the rewards the Venetians received from the Empire, and what were the implications of the chrysobull (Imperial decree) issued in 1082 for the future political and economic relations between the two nations? I will also examine the continuation of the alliance into the twelfth century and see how their relations developed. What caused the rivalry between them and set them down a course that would lead to the Fourth Crusade?

The relationship between the Venetian Republic and Constantinople may have been affected by the sentiment of long tradition – in theory, both parties had close ties since the fifth century, with the latter becoming a part of the Byzantine Empire during Justinian’s expeditions against the Ostrogoths in the second half of the sixth century. But it was based more firmly on realism. Trade was, perhaps, the most significant factor that brought these two parties together centuries ago, and for a good reason. Constantinople and the Byzantine ports of the eastern Mediterranean were the treasure houses of Venetian trade. The people of Venice took natural to the sea and islands and settlements like Cittanova, Heraclea, Malamocco and Torcello became great trading stations long before the end of the eleventh century. Along with the Campanian city of Amalfi which, by the mid-eleventh century had reached the peak of its commercial activity with North Africa and Spain, were the two main trading partners of the Empire in continental Italy.


The Venetians quickly adapted to the larger role of middlemen between the east and west. Byzantine merchants would bring luxury goods from the east to the markets of Torcello and Venetian traders would then distribute them in the west – in Italy, France and Germany. The Byzantines would take payment in the form of timber for shipbuilding, of slaves, metal, salt and fish, products that formed the staple diet of these islanders. And in 992 comes the first military-commercial agreement between Byzantium and Venice, signed by Basil II and Peter II Orseolo (991-1009), by which Venice promised naval assistance whenever the Byzantine Emperors would plan to send an army in southern Italy in exchange for significant trading privileges in Constantinople and Abydos. But what prompted both parties’ common interest to keep the Adriatic Sea clear of rival naval activity? The answer is geography and trade routes!

Map of the Adriatic Sea by Coronelli in 1691.

To and from Venice, voyages both up and down the Adriatic Sea were made invariably along the Balkan coast unless a ship had business in one of the Italian ports. The Balkan coast has a large number of islands and ports for refuge and supplies, is backed by high mountains and there are, generally, no dangerous shallows to hamper the approach of a ship. For the Venetians the many islands and ports possessed or dominated by the city in the lagoons on the Balkan coast from the eleventh century provided secure shelter and logistical facilities for their shipping. The sea-routes as far south as Ragusa lay amongst the islands and channels very close to the mainland, while south of the straits of Otranto lay inshore of Corfu, Cephalonia and Zante, all of which had their main medieval harbours on their east coasts.

To secure these sea routes that formed the life-line of its trade with the Empire, Venice had to exhibit its might against any enemy naval activity that threatened to disrupt the normal flow of goods to and from its ports. This was made clear as early as the mid-9th century when Doge Orso I inflicted a defeat on the Arabs of Bari in 871 just off the coast of Taranto; the Slav pirates operating from some Dalmatian ports throughout the 10th century were finally neutralised in the year 1000, while Venice’s sending of a mission to relieve Bari once again from the Arabs of Sicily in 1004 proved not only its capability to conduct its own foreign policy but also its resolve to keep both coasts of the Adriatic in safe hands. But what was the threat that the Normans posed for the Venetian trade in the second half of the eleventh century?

Robert Guiscard is claimed by Pope Nicholas II as a Duke (Illustration of the Nuova Cronica des Giovanni Villani)

The Normans in Italy

Since their emphatic victory over the papal army of Leo IX at Civitate in 1053, Norman expansion in continental Italy had reached its peak in 1071 with the three year siege and eventual capitulation of the city of Bari – capital of the Byzantine Catepanate of Longobardia. One of the greatest challenges that the Normans had to face since their arrival in Italy, the transportation of a large armed force by sea, was also overcome in May 1061 when a Norman force under the leadership of Robert Guiscard and his brother Roger landed near Messina in Sicily – a feature of great significance for the evolution of military thinking in the Mediterranean that further enabled them to impose a naval blockade in Bari and Palermo (the capital of Muslim Sicily). With the Normans holding the Italian side of the Adriatic, they could threaten the straits of Otranto. But their ambitions went further than that.


In 1074 a Norman Count, Amicus II of Molfetta and Giovenazzo attacked the Dalmatian coasts and allegedly even managed to capture the Croatian King Kresimir, with the only option left to Venice being the launch of a naval expedition to flush him out. But although Amicus was a freebooter, the threat posed by Robert Guiscard’s plans was much greater. Although he advertised his expedition as a “restoration mission” for the deposed Byzantine Emperor Michael VII, that also had the full backing of Pope Gregory VII, “He [Guiscard] was always thinking out some more ambitious project […] and dreamed of ascending the throne himself,” as Anna Comnena writes in The Alexiad. The Imperial Crown is certainly considered one of Robert Guiscard’s ambitions, influenced by the Byzantine culture, language, state organization and economic prosperity, but it was mostly the Empire’s diplomatic involvement in the Apulian rebellions of the 1060s through the governor of Dyrrachium and the quest for more lands for the land-hungry Apulian lords that drove the duke to launch his Illyrian campaign.

Before arriving outside the walls of Dyrrachium in June 1081, Robert Guiscard had already taken the capital city of Corfu – along with the port on the opposite Epirotic coast, Butrinto – probably intending to have it as a forward supply base, while another side-expedition occupied the port of Vonitsa (Bundicia), further south into the Amvrakikos Gulf. The loss of these forward bases, along with the threat posed against Dyrrachium – the port of entry for the Via Egnatia that led through Thessalonica and Adrianople to Constantinople, and a city that also had a large population of Venetian and Amalfitan tradesmen, were very worrying developments for the Venetians. They could not permit them to have a free reign in the Adriatic and severely disrupt their trade with the east.

For the Empire, the Norman invasion of Illyria happened to coincide with a period of great military decline, a result of the defeat at the Battle of Manzikert in 1071 and the replacement of the old thematic and tagmatic units with mercenaries. The newly crowned Emperor, Alexius I Comnenus, an able tactician and experienced in fighting with and against western soldiers in the previous decade, took immediate steps to deal with the threat posed by Guiscard’s armed forces. Concluding a peace treaty with the Seljuk Turks – thus recognising that the latter posed a more serious threat and had to be dealt with in the long-term – he understood that his first move should be to cut the Norman communication with Italy and trap the landing force from its main bases in Bari and Otranto.


In theory, the role of intercepting any Norman invasion fleet would probably have been assigned to the provincial fleets of Dyrrachium, Cephalonia and, perhaps, Nicopolis, that consisted of rather light ships not suitable for open-sea expeditions. But the major naval bases in Cephalonia, Dyrrachium and Corfu had been abandoned, thus allowing only a small squadron of ships to patrol the area with no immediate effect. The years when Constantinople could launch large-scale expeditions against Crete (961), Cyprus (965) and Sicily (1038) have come and gone. After 1025, the pax romana that had been established in the Byzantine seas turned the attention of the central government away from the seas, prompting a steady decline in the strength of both the Imperial and thematic fleets. The final blow came with their transformation from military to administrative provinces in the 1040s, as it was the case with the land themata in Asia Minor.

Alexius’ decision to call for the Empire’s faithful ally, Venice, was brought by reality and – perhaps – desperation. The Byzantine government was not only considering Venice as an early warning beacon for threats coming from the north and some sort of a buffer zone for its Dalmatian territories. It had used the Venetian fleets to patrol the Adriatic, transport Byzantine troops to and from Italy and Sicily and provide naval support to Imperial expeditions in the same region as early as 827 when the Muslims were besieging Syracuse. And it was the Empire’s strategic position, obliging her to fight in two distant operational theatres of war – Asia Minor and the Balkans, along with its limited resources in money and manpower that prompted the use of diplomacy, bribery, fraud and other means to avoid war! In other words, the Byzantines were more willing to have others to fight their wars than send naval detachments in a region far away from their main operational theatres closer to the capital.  And as long as they provided them with rewards, the Venetians were more than willing to play that role. But what evidence do we get from our chronicler sources about Venice’s involvement in the siege of Dyrrachium in 1081 and 1084?

Image by MapMaster / Wikimedia Commons

Fighting the Normans

Our two main sources for the naval battles between the Venetians and the Normans in 1081 are Anna Comnena, the daughter of the Emperor Alexius writing between 1143-48, and Geoffrey Malaterra, a monk commissioned by Roger Hauteville to write the conquest of Sicily by the Normans in the later years of the 11th century. Malaterra’s sources for his work, for he was not an eye-witness himself to the events he describes in his history, were primarily oral, gathered from people who had witnessed the events, although we cannot be sure whether he had access to any archival material. Anna may not had been an eye-witness of the events but her position in the Imperial Court brought her in daily contact with many leading figures of the Empire. Apart from her father and Emperor, she also had access to several other important officials like her uncle and governor of Dyrrachium George Paleologos, while she was able to gather useful information from eye-witnesses of the events and gain access to archive material in the capital.

The accounts of the ensuing naval battle between the Venetian squadron that arrived in the Illyrian waters, sometime in late July or early August, and the Normans are rather contradictory. According to the Alexiad, when the Venetian fleet arrived north of the besieged city, they refused battle on the first day. And while they prepared the fleet during the night for the next day’s naval confrontation, having wooden towers erected on the main mast and manned with experienced men, there was a fierce battle between the two fleets. But the Normans were unable to break the solid Venetian “sea-harbour,” meaning the defensive formation where the biggest and strongest vessels were tied tightly together providing shelter for the smaller vessels, and they were eventually routed.


Malaterra had a rather different story to tell, presenting the Venetians as a cunning and crafty enemy. The Normans immediately attacked the Venetians once they realised their arrival in Illyrian waters, and after a most violent naval battle, by sunset the Normans seemed to had won the day. The Venetians, promising to surrender the next day asked for a truce, but during that night they erected wooden towers in the ships’ main masts and made their vessels lighter and, thus, more manoeuvrable. By sunrise, the re-organised Venetian squadron attacked the unprepared Normans, forcing them to retreat while they were breaking the naval blockade imposed to the city, making effective use of the Greek fire.

We cannot be certain as to which of these accounts is the most accurate, but it seems more likely that Anna’s story is closer to the truth if we think about not only her sources – her father and her uncle – but also the fact that she is much better informed about the Norman operations in the Balkans as a whole than any of her Italian counterparts.

Whatever the case, the role played by the Venetian navy in 1081 was paramount for the imposition of a naval blockade on Guiscard’s expeditionary force, cutting them off from their bases in Italy. If Alexius had chosen to impose a land blockade as well, like he did twenty-six years later, the outcome of the campaign would have been different. The Venetians had promptly and willingly played their part as Imperial allies, but it was no fault of their own that Dyrrachium eventually fell to the Norman duke. And while Guiscard was busy in Italy and his son was campaigning freely in Greece, they sent another fleet to dislodge the Norman garrison from Dyrrachium – failing though, but establishing a base in the lower part of the city to keep their enemies occupied.

Corfu Old Fortress – Photo by Kurt Bauschardt / Flickr

For the second Norman expedition in the Balkans Robert Guiscard departed from Brindisi at the end of September/early October 1084 with a fleet of 120 ships, landing at the northern port of Cassiopi in Corfu just like he had done in 1081. The only difference this time was that he found a joined Venetian-Byzantine fleet waiting to attack him. We are not informed about the number of ships that were sent by the Doge, but we should not expect a large expeditionary force since it only took the Venetians a few weeks to prepare and sail south. Our sources use vague terms like triremes and naves to describe the consistency of the Venetian fleet, although by reading the Alexiad we understand that both large vessels, like chelandia or types of dromons, and lighter and faster ships, like the galeai, would have been deployed.

We follow Anna Comnena’s narrative about the naval engagement off Cassiopi in the north-eastern side of the island of Corfu. During their first encounter, the Venetians managed to rout the Norman squadron, but Anna gives us few if any details about the course of the battle. Three days later the allied fleet attacked the Normans once more, trying to inflict a significant blow upon the relatively small Norman squadron of warships, but again their victory was not decisive enough to force Robert Guiscard to retreat back to Avlona.

This time, however, the Venetians made the grave mistake of underestimating the enemy’s losses and they sent envoys to Venice to announce the news. With their small and fast ships sent back home, the Normans attacked. Completely surprised, the Venetians barely had the time to tie their ships together and form the pelagolimena, the defensive formation seen three years before at Dyrrachium. The Norman ships, being made much lighter the day before, took full advantage of their speed and mobility and overwhelmingly defeated the allied fleet.

For Venice this was a crushing and humiliating defeat. Anna mentions around 13,000 casualties, which is surely an exaggerated figure, and 2,500 prisoners. Lupus Protospatharius, who’s Chronicon covers the period between 805-1102, writes about more than a thousand men killed in action, five ships captured by the Normans and two which were sunk with their entire crew, a much more realistic estimate for the Venetian casualties. As for the treatment of the prisoners by the Normans, Anna reports: “Many of the prisoners were treated with hideous savagery: some were blinded, others had their noses cut off, and others lost hands or feet or both.” There was no precedent in Robert Guiscard’s behaviour against prisoners of war, neither at Dyrrachium three years ago nor against the Bariots, the Palermitans or the people of Naples in the 1070s. Probably the Duke wished to send a warning to the Venetians never to launch another naval campaign against his army. This gruesome method of psychological warfare proved very effective by Roger after the Battle of Misilmeri (1068), when hardly any Muslims survived to bring the news of their defeat to the inhabitants of the Sicilian capital.

The chrysobull

Painting of Alexius I, from a Greek manuscript in the Vatican library

In the longer term the Norman victory was of no importance, as Guiscard’s expedition reached an abrupt end with the latter’s death in July 1085. But the Venetians expected their reward for all the sacrifices they had made as allies of Byzantium. The text of the chrysobull which Alexius had promised to them in 1081 exists, albeit in an incomplete Latin version contained in later documents and in a brief summary in the Alexiad. Although there has been a debate regarding the dating of the document to 1082 or 1084, its content is the most comprehensive and detailed charter of privileges that had ever been granted to the Republic by a Byzantine Emperor, thus forming the corner-stone of the Venetian colonial Empire in the Eastern Mediterranean.

The chrysobull of 992 may had granted the Venetians the privilege of having to pay their dues only to the highest official of the state, but now they were getting a permanent colony of resident traders on the Golden Horn, a number of buildings, churches and other properties were designated as Venetian and they also earned the right to trade in all parts of the Empire free of any charge, tax or duty payable to the Imperial Treasury. The chrysobull made the Venetians feel that their sacrifices in the war against the Normans were worth the cost. It was a document designed to bring them back in Byzantine orbit, not as faithful subjects but rather as dependable allies by giving them the ability to open the door to the wealth of Byzantium and the Orient; and they made sure that these privileges were renewed and extended at intervals.

Until the eve of the launching of the Fourth Crusade, Venice and Byzantium were partners in an alliance that had grown steadily for centuries. They both needed each other, though for different reasons. The Byzantines saw Venice as an early warning beacon and a sort of a buffer zone in the Adriatic, while its ships provided valuable transport means for Imperial expeditions and patrolled the Adriatic – tasks which the Byzantine navy was growing increasingly incapable of performing after the second half of the 11th century. Venice’s economy relied on trade and all of the trade routes passed through the Adriatic Sea and the Aegean to Constantinople, the capital and economic heartland of the Byzantine Empire – the gateway for products coming from the Orient that Venice was distributing in the west. The Doges were keen to keep the Adriatic free from enemy activity that could hamper their trade, but more and more on their own behalf rather than for the sake of the Byzantines. Their fleet was sent to assist the Imperial forces on several occasions since the mid-9th century, with their naval campaign against the Normans in Dyrrachium in 1081-4 earning them by far the most significant concessions ever made by a Byzantine Emperor to the date.

Crude tradesmen as they were, the Venetians were always thinking twice as to which side to take and being careful not to alienate a party with which they wish to conduct business with. Their reluctance to join the cause of the First Crusade as they were trading with both Byzantium and Fatimid Egypt is characteristic. Indeed, the stable markets of Constantinople and Alexandria seemed preferable than the uncertainties of the markets in the Middle Eastern ports. They also seemed quite adaptable to the changes in the pattern of alliances in the Adriatic, keen to demonstrate to both the east and west the fact that they were able to conduct their own foreign policy. It was they who proposed an anti-Norman coalition to the Byzantine Emperor John Comnenus in 1136, “suffering great injustice by the piratical attacks of the Muslims of Jebba” in the Tunisian coast who were paying tribute to the Normans, but really worrying about the resurgence of the naval power of the Sicilian Normans in the Adriatic, the central Mediterranean and Antioch.

Venice, from “Supplementum Chronicarum”, 1491

However, according to charter evidence, it was Roger II who bought them over with trading privileges in 1137, thus detaching them from the alliance which by that time had also included Lothair of Germany. Ten years later, once again due to the Norman threat in the Adriatic, they detached a naval squadron to participate in the Imperial campaign to dislodge the Norman garrison installed in Corfu, with some 13th century Venetian chroniclers reporting significant number of vessels and siege machines being brought to the island. But in 1154, they advertised their neutrality by negotiating treaties with William I of the Kingdom of Sicily and Frederic Barbarossa of Germany, much to the surprise of Manuel Comnenus.

Their greatest asset in Byzantium was their commercial quarter in Constantinople, the centre of their trading power in the capital which was established by Alexius’ chrysobull in 1082. It was there, however, that they rubbed shoulders with the Byzantine people and earned a reputation for arrogance. Indeed, we read Choniates’ description of the Venetians – “they are beggars, cunning in thought … and surrounding themselves with wealth, they pursue insolence and impudence” – which is not as objective as we might expect but quite characteristic of the Byzantine view of this sea-faring people. Emperor Manuel (1143 – 1180) had extended the limits of their quarter in Constantinople after they had complained that the part allotted to them by his predecessors was not big enough; the number of Venetian traders and merchantmen had grown significantly in the last century, although not as much as the figure of 10,000 given by Doge Dandolo. The Emperors hoped that the Venetians would be restricted to the areas allocated to them – some sort of a ghetto – like the residents of other naval powers like Amalfi, Genoa and Pisa. But this did not happen.

A Fraying Alliance

The mutual animosity between the Byzantines and the Venetians was made obvious during the reign of John II (1118 – 1143). For the Byzantine Emperors, the commercial agreements and privileges dispensed to the Republic were the means of perpetuating a valuable partnership for mutual assistance against the Muslims and the Normans of the Mediterranean. And it was John’s denial to renew his father’s agreement with Venice that brought to the surface not just the Emperor’s frustration for the lawlessness and arrogant behaviour of the Venetians, but his will to underline the fact that Byzantium was the senior partner in the arrangement and not an equal member. Eventually, the Doge’s punitive naval expeditions in the Ionian and the Aegean seas in 1124 with some hundred ships and 15,000 men forced John to concede that the Byzantine forces were not up to the task to either patrol the Byzantine Seas or control the Venetian navy. It seemed better to make peace with that power in the hope that it could be called as an ally in the future, than risk a war!

Alexius Comnenus had given the Venetians the right to trade freely in Byzantine ports in Greece and Asia Minor. John II had extended that right to the islands of Crete and Cyprus, a concession which facilitated trade with Egypt and the Middle-East, perhaps unwittingly opening the door to a vision of almost unlimited and highly privileged trade and profit for Venice in the eastern Mediterranean. The renewing of the commercial agreements may have fallen on the discretion of each Emperor, by the third quarter of the 12th century it seemed clear that Byzantium was losing control of its one trusted and faithful ally, which can be more than vividly demonstrated by the events that unfolded in the capital in 1171 and 1182. And although the three chrysobulls issued by Isaac II (1185 – 1195, 1203 – 1204) in 1187 did little to redress the relations between the two parties, the balance of power was now weighted in favour of Venice.

Emperors like John II and Alexius III (1195 – 1202) tried to offset the power of Venice by signing trading agreements with Pisa and Genoa, but their attempts were in vain. Although Venice’s greed was growing, its patience was steadily running low, with the Fourth Crusade offering them the opportunity to right the wrongs done to their profit and honour. This was, indeed, the most expensive and risky gamble the Venetians had ever taken. But it paid off unbelievably well – for fifty six years they did not have to worry about protecting their trade agreements with the Empire. It was simply, as David Nicol puts it, a fruitful combination of state and private enterprise which amassed untold wealth to the city of Venice. For how long it lasted, the Latin Empire of Constantinople was by far the most profitable investment the Venetians had ever underwritten.

Georgios Theotokis: Ph.D History (2010, University of Glasgow), is historian specialising in the military history of eastern Mediterranean in Late Antiquity and the Middle Ages. He has published numerous articles and monographs on the history of conflict and warfare in Europe and the Mediterranean in the Medieval and early Modern periods. His first monograph was on the Norman Campaigns in the Balkans 1081-1108 (2014), while his second book on the Byzantine Military Tactics in Syria in the 10th century came out in October 2018. He has taught in Turkish and Greek Universities; he is currently a postdoctoral researcher at the Byzantine Studies Research Centre, Bosphorus University, Istanbul. Click here to read more from Georgios Theotokis.

Top Image: Venice, Constantinople and the Adriatic and Mediterranean regions as seen in the Catalan Atlas.