A conflict between the Genoese and the Venetian merchant communes in Acre (mod. ‘Akko, Israel) that escalated into a civil war that embraced the whole of the kingdom of Jerusalem.
The conflict developed out of rival claims by the Genoese and the Venetians to the monastery of St. Sabas, which lay on the boundary between their respective quarters in the city, and was fueled by their competition for the maritime trade of the Mediterranean. Early in 1256 the Genoese seized the monastery and attacked the Venetian quarter with the support of the Pisans. They were repulsed, but siege engines were set up with which the Italians bombarded each other.
The kingdom of Jerusalem was divided by the conflict. John of Arsuf initially backed the Genoese, while some barons, led by John of Jaffa, favored the Venetians. Philip of Montfort, lord of Tyre and Toron, used the opportunity to expel the Venetians from Tyre (mod. Soûr, Lebanon) and allied himself with the Genoese. In July 1257 the Pisans changed sides to join Venice. The fraternities in Acre sided with the Venetians, as did the Templars and the Teutonic Knights, while the Hospitallers supported the Genoese. The communes from southern France opposed the Genoese, and consequently the Catalan communes backed them.
The Venetians gained ground when John of Jaffa successfully manipulated the regency laws to bring Plaisance of Antioch to power in the kingdom of Jerusalem. As bailli (regent) she ordered the Crown vassals to support Venice. Both sides were reinforced by new arrivals from Europe, and the struggle continued both on land and at sea. A Venetian fleet under the command of Lorenzo Tiepolo broke the Genoese blockade of Acre and regained possession of their quarter. In June 1258 Philip of Montfort, with the support of the Hospitallers, led an army south to attack Acre while the Genoese launched an assault from the sea. The Venetian and Genoese fleets clashed, and the latter were defeated, losing many men and galleys, and Philip and the Hospitallers were forced to withdraw.
The position of the Genoese in Acre had become untenable, and they abandoned the city in favor of Tyre. The conflict had destroyed much of Acre, damaged its trade, and exacerbated the factional divisions within Outremer.