In December 1255, Marco Gradenigo was sent with three
galleys (seven, according to
Andrea Dandolo) to reinforce the Venetian garrison of the City of Negroponte (modern
Chalkis). The city had been captured by the local
Lombard lords of Euboea (the '
triarchs') with Venetian assistance, against the claims of the
Prince of Achaea,
William II of Villehardouin, thus sparking the
War of the Euboeote Succession. As Villehardouin's forces recovered Negroponte, Marco Gradenigo laid siege to the city, an affair which dragged on for thirteen months before the city capitulated. An Achaean counterattack was repulsed by Venetian pike-wielding infantry sallying forth and defeating the famed Achaean cavalry before the city's walls. By June 1256, Marco Gradenigo replaced
Paolo Gradenigo as the resident Venetian governor (
Bailo of Negroponte). In this capacity, he organized an alliance with the triarchs against the hegemonic claims of Villehardouin. Many other rulers of
Latin Greece, including the
Duke of Athens,
Guy I de la Roche, joined this anti-Achaean league. Ultimately, the alliance failed, as Villehardouin defeated the allied forces at the
Battle of Karydi in May/June 1258, resulting in a negotiated end to the war in 1259. By August 1258, Gradenigo had been replaced by
Andrea Barozzi, and was appointed as
Podestà of Constantinople, governor of the Venetian colony in
Constantinople, capital of the
Latin Empire. In July 1261 Gradenigo led his fleet of thirty ships to capture the island of
Daphnousia in the
Black Sea, held by the
Empire of Nicaea. His absence from Constantinople allowed the
recapture of the city by the Nicaean general
Alexios Strategopoulos. The Venetian fleet returned from it unsuccessful attack on Daphnousia only to find the city taken, the Venetian quarter in flames, and the Latin population fleeing. Gradenigo decided not to risk a landing, but instead took on the refugees, including the Latin Emperor,
Baldwin II, and brought them to safety in Negroponte. In 1264–1266, Gradenigo held naval commands in the
conflict against the
Republic of Genoa, and led a squadron of ten galleys under
Jacopo Dondulo in the crushing Venetian victory at the
Battle of Trapani in June 1266. In 1269, he was a
ducal councillor. In 1270, he served as one of the two Venetian commanders in the war with
Bologna in 1270. In 1272, he served again as ducal councillor. ==References==