Carthage had paid off its indemnity to Rome, imposed fifty years before at the end of the First Punic War, in 151 BCE and was prospering economically, but was no military threat to Rome. Nevertheless, there had long been a faction within the Roman Senate that had wished to take military action against Carthage. Using the illicit Carthaginian military action as a pretext, Rome began preparing a punitive expedition. Carthaginian embassies attempted to negotiate with Rome, which responded evasively. The large North African port city of Utica, some 55 km (34 mi) north of Carthage, defected to Rome in 149 BCE. Aware that Utica's harbour would greatly facilitate any assault on Carthage, the Senate and the People's Assembly of Rome declared war on Carthage.