An impressive fortification system on the northern border of the Genoese Quarter at Crusader-period Acre was discovered, comprising a defensive wall built of bossed ashlars and incorporating arrow slits, a fortified gate leading to the quarter through a vaulted passageway and a projecting tower with two levels of arrow slits. The gate and parts of the passageway were blocked, apparently during the Crusader period, as a consequence of the Saint Sabas War. This war broke out following a dispute between Venice and Genoa over ownership of a monastery located on the border between their quarters, near the port, which was rooted in their struggle over control of the harbor of Acre and the eastern Mediterranean lucrative maritime trade. Written sources indicate that the outcome of this fierce conflict was the expulsion of the Genoese from Acre and the blocking of their quarter. The presence of a blocked gate and the abandoned state of the area are physical evidence of the aftermath of the War. These remains, well-preserved within eighteenth-century Ottoman buildings, do not only shed light on the nature of the Genoese Quarter’s northern fortified borderline but also provide the first concrete material evidence of defense, power and control by the Italian communes in the maritime hubs of the Crusader states.