The Byzantine Empire
Manuel I Comnenus (1143-1180)
Manuel was concerned early in his reign with Sicily. In 1143 he considered an arrangement whereby King Roger II was to marry his son to Manuel's daughter, but that came to nothing. During the Second Crusade, Roger attacked Corfu, which is one reason why the Greeks were unable to provide substantial help to the Crusaders. In fact, Manuel had to enlist the help of Venice in his fight against Sicily, whereby Venice gained further trading privileges in the Empire.
Manuel was able to drive Roger back in 1148, but only at great cost. Part of the loot the Normans took away with them was a group of silk weavers, bringing that skill to the West for the first time. Manuel spent the next few years trying to assemble a counter-invasion of Italy. He and his long-time ally King Conrad of Germany were planning an expedition for 1152, but Conrad died that February and the plan fell through.
Conrad was succeeded by Frederick Barbarossa, who was much less friendly toward Byzantium. He played along from time to time, however, so Manuel continued to hatch plots against Sicily. In 1155, the Greeks actually invaded Apulia, but they did not get very far, and were defeated at Brindisi. They continued to operate in southern Italy for a few years, but Manuel came to terms with King William of Sicily in 1158 and withdrew the Byzantine troops from Italy.
After this, Manuel did not try open invasion against his old enemies, but he continued to use diplomacy. His main effort was to ally with the papacy, for the popes often regarded either Sicily or the German Emperor, or both, as their principal enemy. One item he offered was the prospect of a union of the Churches, a diplomatic prize that would get offered almost any time the Byzantine emperor sought an alliance with the papacy.
Manuel also sought allies among the Italian city-states, but this ground was even more treacherous than southern Italy. Venice, Pisa and Genoa were all rivals, but all had a significant trading presence in the Empire. To ally with one would be to make enemies of the others. Moreover, alliance with any of these meant trade concessions, and the Greeks hated the Italian merchants who occupied whole sections of their towns, including Constantinople itself. So, every move Manuel made in this direction aroused the anger of his own people.
Manuel was close to Venice in the first part of his reign, but they had a falling out in the 1160s. There had been quarrels and skirmishes in Dalmatia (1166), arguments over the extent of privileges, and even street fighting in Constantinople between Venice and Genoa. In 1169, Manuel made a treaty with Genoa, and in 1170 he made one with Pisa.
Then, on March 12, 1171, Manuel ordered the arrest of all Venetians everywhere within the Empire. All their goods were confiscated. The Doge of Venice sent a fleet to attack cities in Dalmatia and some desultory fighting resulted, but despite the dramatic gesture, relations between Venice and the Empire were gradually restored. By this time, Venice understood that Constantinople was a key to its wealth and to its ability to compete against Genoa and Pisa; she could not afford a pitched war. Conversely, a war with Venice would be more expensive than the Empire could manage. Consequently, both sides gradually backed down over the next decade and the situation in 1180 was much the same it had been in 1170. One legacy persisted, however: bitterness. The Greeks still hated the Venetians, restored to their former arrogance. And Venice was bitter over yet another example of Greek duplicity and betrayal, this one having struck at the very heart of the city's existence. They were never again more than uneasy allies.
Manuel was able to stabilize his northern frontier by a marriage alliance with Hungary. Hungary and Byzantium had long been enemies, clashing over the Serbian border territories. In 1164, Manuel agreed to recognize Stephen III as King of Hungary, renouncing ancient Byzantine claims, in exchange for which Stephen's son Bela would be married to Manuel's daughter Maria. Bela would rule Dalmatia, Croatia, Bosnia, and Sirmium while Manuel lived, and would succeed as emperor.
The arrangement was thrown over in 1169, though, with the birth of a son to Manuel. Bela and Maria were betrothed but not yet married, so that relationship was dissolved. Bela kept his lands but would no longer succeed to the Empire. The Hungarian was eventually married to Agnes of Châtillon, daughter of the infamous Reynauld and Constance of Antioch, and with Greek help succeeded to the Hungarian throne in 1173.
Manuel was initially successful in the east, but then suffered a dramatic reverse. He moved into Cilicia in 1158, reasserting Byzantine authority there, and the following year inflicted a defeat on Reynald of Antioch. He was so far successful in Syria that we was able to restore a Greek patriarch at Antioch in 1165. He remained on good terms throughout his reign with King Baldwin III of Jerusalem.
But when Manuel tried to move against the Turks in Anatolia, disaster struck. He himself led a large Byzantine army in 1176 against the Seljuks and Kilij Arslan II. His entire army was trapped in the pass of Myriokephalon and was prevented from complete destruction only because the sultan offered terms. He was forced to accept the Turks as allies and to forswear aggression against them, as well as to pay a huge sum of money. Myriokephalon marked the end of Manuel's military activities and struck a severe blow to Byzantine prestige.