The Byzantine–Venetian War of 1171 was fought between the Byzantine Empire and the Republic of Venice as a result of the Byzantine imprisonment of Venetian merchants and citizens across the Empire. 10,000 Venetians were imprisoned in the Byzantine capital, Constantinople, alone. Despite Doge Michiel's apparent will to pursue a peaceful solution, outrage in Venice itself swung popular opinion in the favour of full scale war against Byzantium. Doge Michiel had no choice but to set out for war, which he did in mid-late 1171. After indecisive battles in Euboea, Michiel was forced to withdraw his fleet to Chios. After a number of months on Chios, whilst waiting for a Venetian embassy to be received in Constantinople, plague began to set in. However, the emperor of Byzantium, Manuel I Komnenos, was well aware of the plague, and continued to stall negotiations. The Venetians attempted to move from island to island to avoid the plague. Doge Michiel's efforts, however, were fruitless, and in May 1172, he returned to Venice with what was left of the fleet. The Venetians were decisively defeated.
Background
Relations between the Byzantine Empire and the Republic of Venice had taken a steep turn for the worse during the 12th Century. Between the extensive reforms of the Venetian church and the refusal of Venice to assist Byzantium in an invasion of southern Italy, the Byzantine emperor, Manuel I Komnenos, was increasingly hostile towards the Venetian government. Firstly, Manuel began to cultivate relationships with the main commercial rivals of Venice: Genoa and Pisa. He also granted these other Italians their own quarters in Constantinople, very near to the Venetian quarter, effectively elevating the groups to the same social status within the Empire. One day a mob of Venetians effectively ransacked the Genoese quarter, looting and killing the Genoese, until the imperial guard arrived to restore order. This blatant act of disobedience convinced Manuel that Byzantium no longer needed Venice as an ally; Genoese strength now matched that of Venice's, and it seemed that Genoa could just as effectively protect Greek waters as Venice, and without the apparent arrogance. In early 1171 Manuel began to develop his plan for retribution. He sent secret messages to officials across the empire to imprison and confiscate the property of every single Venetian they could find. The plot was kept a secret, while Manuel continued to assure Venetian ambassadors, dispatched by Doge Michiel after the looting of the Genoese quarter months earlier, that Byzantium would not seek to exact revenge upon Venice. The ambassadors would return to Venice with the good news. On March 12, 1171, Manuel set his plan in motion. Venetian men, women, and children across the empire were imprisoned, their property confiscated and goods held by local Byzantine officials. Only a handful of Venetians escaped. When the news arrived in Venice, it was met with shock, outrage, and, at least on the part of the Doge and the ambassadors, embarrassment. Doge Michiel summoned his board of high councillors, the sapienti, for a meeting. They overwhelmingly urged the Doge to proceed with caution. Many of the reports they were receiving from Byzantium were fantastical, and they thought it wise to first ascertain if many of these facts were true, and then assess the damage. The Doge agreed with this course of action. However, as Michiel began to lay out his plans to attempt to solve the issue diplomatically, a convoy of 20 Venetian vessels, a few lucky stragglers who had managed to escape the arrests, arrived in the Venetian lagoon. They told great stories of the Byzantines' betrayal, and, as citizens became to pour out of their houses to listen to the stories, the sailors were able to stir up the rancor of the populace, effectively motivating them to seek revenge. The people gathered outside of the Ducal Palace, urging the Doge to undertake a retaliatory strike against the Greeks. Michiel had little choice, and, against his and the sapienti's better judgment, he set out for war.
Michiel sailed his armada first to Dalmatia in order to quickly reinforce Venetian dominance there. The fleet then sailed around the Peloponnese and into a port at Negroponte. There, the fleet disembarked and began to lay siege on the regional capital of Euripos. It quickly became clear that the city would fall, and, seeing this, the Byzantine governor in Negroponte organized a meeting with the Venetian leaders. In this meeting, the Venetians made it clear they wished for peace. So, in exchange for the Venetians lifting the siege on Euripos, the governor agreed to send a message to Constantinople urging the Emperor to make peace. While waiting out a response from Manuel, Michiel ordered his fleet to withdraw to the eastern Aegean island of Chios, where they would wait out the winter waiting for Manuel's response. Manuel, however, had no mind for peace. He refused to see Michiel's envoy and, in return, dispatched an ambassador to the Venetian fleet in Chios, who conveyed to the Venetians that the emperor hoped to make peace, and that perhaps by sending another envoy to Constantinople, a settlement might be reached. Manuel's real plan was to forestall Venetian advancement while he took the time to organize his forces and establish a fleet capable of confronting the Venetians. His ruse worked better than expected. The Venetians sent another envoy to Constantinople, and, shortly after the embassy departed, a devastating plague broke out in the Venetian camp, which killed thousands within the first day. Opinion within the Venetian camp had also begun to sway against the Doge, who had, in their first encounter with Byzantine forces, peacefully withdrew without dealing any real damage to the enemy in favor of a diplomatic solution and, now, after months of waiting, had allowed for a terrible plague to set in while waiting for yet another possible diplomatic solution. In March, the fleet moved to the island of Panagia, but the plague followed. Later that month the Venetian delegation returned from Constantinople with bad news: they had once again been denied an audience with Manuel, however, that had been promised that if the Doge sent a third embassy, they would be received. At this point, the Doge was in a bad situation. More of his men were dying every day and the plague was hardly letting up. He had received whispers of a plan for a Byzantine attack on the Venetians at sea or on Chios, so he hardly believed Manuel intended to make peace with him. However, if he was able to shake of the plague, Michiel's fleet was still large enough to cause trouble for Byzantium in the Aegean. He hoped that with yet another embassy, and that threat still alive, it would be possible to persuade Manuel to at least release the Venetian prisoners. He dispatched Enrico Dandolo and Filippo Greco to the Greek court. Michiel then moved the fleet first to Lesbos and Skyros. Nothing slowed the plague down. As more and more Venetian soldiers died in camp, it became increasingly clear that the fleet no longer posed any threat to Byzantium. In fact, the fleet was now itself in danger. The remainder of the depressed Venetians ordered their Doge to take them home.
Aftermath
With the utter destruction of their fleet, the Venetians sailed home in disgrace. They limped into the Venetian harbor in May 1172, and public opinion immediately swayed against the Doge. Blamed not only for the loss of lives and ships, but for the utter disgrace and humiliation of Venice, a mob began to form in the street. The Doge had wasted the Venetians' time with useless legates and envoys in a fruitless effort to solve a military issue diplomatically, and tens of thousands of Venetians were still imprisoned across the Byzantine Empire. Michiel tried to reason with the mob, however, he found himself alone, and attempted to flee to a religious sanctuary in the city where he was eventually overtaken and stabbed to death by a man named Marco Casolo. This killing did nothing to quell the angers of the Venetian people; if anything it only depressed them. Michiel's assassin was then publicly executed, but this, too, did nothing to assuage the Venetian people, who were now overcome with regret. The death of the Doge resulted in the election of 11 men to a commission, made up of the old sapienti, who would in turn elect to next Doge. The disastrous defeat of Venice in this war was one of the greatest military blunders in the city-state's history, and permanently altered Venice's position on foreign affairs. A formal truce between the two empires would not be ratified until 1177, with minor skirmishes continuing until then.
