From Charles Mann’s 1491:
Almost 150 years before Columbus set sail, a Tartar army besieged the Genoese city of Kaffa. Then the Black Death visited. To the defenders’ joy, their attackers began dying off. But triumph turned to terror when the Tartar khan catapulted the dead bodies of his men over the city walls, deliberately creating an epidemic inside. The Genoese fled Kaffa, leaving it open to the Tartars. But they did not run away fast enough; their ships spread the disease to every port they visited.