Tzibus' monopolization of trade in Petra soured Rome's relations with the Lazi, whose king, Gubazes, secretly sought Sasanian assistance against Rome.[3] This occasioned an invasion by a Sasanian army under Khosrow I in 541 and twenty years of war in Lazica, in the course of which Petra changed hands several times. In 541, Khosrow, following an initial unsuccessful assault on the fortifications of the city, captured Petra by sending his troops through a secretly constructed tunnel and destroying the towers, which induced the Romans to capitulate. Khosrow appropriated the riches of Tzibus, who was killed in battle, but treated the Romans of the city with consideration.[6][7]