Finally, the rise of Charles of Anjou in Italy and his hegemonic ambitions in the wider region, which threatened both Venice and the Byzantines, provided additional incentive for both powers to seek an accommodation.

[6] Barred from the Black Sea and Constantinople by her rival, Genoa, Venice now followed a two-pronged strategy of using the Papacy and the threat of excommunication to pry the Genoese away from the Byzantines, and of obtaining the assistance of other Western powers, like Manfred of Sicily, for a campaign against Palaiologos.

[14][15] The Greek and Latin texts of the treaty are preserved in the collection of Venetian diplomatic documents compiled by Gottlieb Tafel and Georg Thomas and published by the Imperial Academy of Sciences in Vienna.

[16] Its main provisions were: The treaty was not ratified by the Doge, for reasons that are unclear: according to Geanakoplos, either the Venetians interpreted Palaiologos' concessions as a sign of weakness, or mistrusted his ultimate intentions, since his desire to restore the Byzantine Empire to its pre-1204 boundaries was obvious and directly affected their own possessions in the area.

[21] Furthermore, as Donald Nicol points out, Zeno still cherished the title, adopted after 1204, of 'Lord of one-quarter and one-eighth of the Empire of Romania' (Latin: dominus quartae partis et dimidiae totius Imperii Romaniae), and would be loath to accept a treaty that recognized him merely as 'Doge of Venice and Lord of Croatia, Dalmatia, and the other places and islands subject to his authority' (Dux Venetiarum et dominator Chroatiae et Dalmatiae et omnium aliarum terrarum et insularum suae, Greek: δοὺξ Βενετίας καὶ ἐξουσιαστὴς Χορβατίας, Δαλματίας καὶ τῶν ὑπὸ τὴν ἐξουσίαν αὐτοῦ λοιπῶν χωρῶν τε καὶ νησίων) and that effectively diminished his standing and reverted the relations between Venice and Constantinople to the status quo before 1204.

[22] Venice may also have hoped to secure, or even augment, her position in the area with the aid of either Manfred of Sicily or the new and ambitious contender for supremacy in Italy, Charles of Anjou, whose ultimate designs on Constantinople were common knowledge—whence his inclusion in the draft treaty by Palaiologos.

[23] Following his decisive victory over Manfred of Sicily at the Battle of Benevento in February 1266, Charles of Anjou became the effective master of Italy, and began to plan for the realization of his ambitions against Constantinople.

[25] Concerned over Charles' ambitions, and with his previous treaty with Venice rendered null and void, Palaiologos was forced to turn again to Genoa, allowing the establishment of a Genoese colony in the suburb of Galata, across the Golden Horn from Constantinople.

[26][27] These developments disquietened the Venetians as well: their trade with the East had suffered considerably following the Byzantine alliance with Genoa, while Charles of Anjou's imperial ambitions in the Adriatic and Greece were a potential threat to Venice's own freedom of access to the Mediterranean.

[48][49] The Venetian stance reflected both their satisfaction, for the time being, with having again secured commercial access in the Byzantine Empire, as well as their disquiet at Charles' policies in the Adriatic, including a recent agreement with Hungary, which had been Venice' traditional rival over control of Dalmatia.

[56] Palaiologos' diplomatic offensive continued with his rapprochement with the Papacy, which alone could either decisively further or thwart Charles' plans, by either supporting his campaign against Constantinople and declaring it a Crusade, or prohibiting it as an attack on a fellow Christian monarch.

[58] Although the Union proved deeply unpopular among the Byzantine Church and populace, it was a "diplomatic triumph" for Palaiologos, as the Pope recognized him as legitimate emperor of Constantinople and forbade Charles to attack him.

[59] Although the Venetian representatives at Lyon had vociferously protested that Venice still claimed its rights in 'Romania', the advantage lay with Palaiologos, and the new Doge, Jacopo Contarini, in 1276 sent envoys to Constantinople to renegotiate the 1268 treaty.

The outbreak of the Vespers had ruined Venetian chances to recover their privileged position, and for the duration of the state of war their trade with the East was interrupted, much to the advantage of the Genoese.