Livy reported that after the "Secessio plebis" of 494 BC, a strike by the common people for political rights, a famine occurred at Rome due to decreased economic activity. Grain buyers were sent to "the people of the Pomptine marshes" and elsewhere to acquire new supplies, but were met with refusal. The Volsci attempted to exploit this momentary weakness by raising an army of invasion, but were struck down by an epidemic, of what sort, or whether historians can conclude to be malaria, remains unsaid. The Romans, buying grain in Sicily, reinforced their colony at Velitrae and planted a colony at Norba, "which thus became a fortified point for the defence of the Pomptine region." In 433 BC, Rome was struck by an epidemic and again sent buyers to the Pontine, this time successfully. Apparently, at least some of the marsh was under cultivation, which the high density of Roman settlements along the two northern roads might lead one to expect.