Taanit, Chapter Three, Mishnah Four
This mishnah continues to discussed localized fasts, the topic begun in yesterdays mishnah.
1) And so too a city which has a plague or [its buildings] collapsethat city fasts and they sound a blast, but those [in the places] around it fast but do not sound the alarm. Rabbi Akiva says: they sound the alarm but do not fast.
2) What constitutes a plague? If in a city that can supply five hundred foot-soldiers and three deaths occurred on three consecutive days, behold this constitutes a plague, less than this is not a plague.
Section one: This section is basically the same as yesterdays mishnah, it just mentions plagues and building collapse as opposed to rain. Just as Rabbi Akiva and the sages debated what the surrounding cities do in the case of drought, so too they debate these cases.
Section two: This section differentiates between a plague and isolated instances of death. For something to be a plague a certain percentage of the people of a town must die within a certain amount of time. The mishnahs answers its question by stating that if the town is large enough to send out 500 foot-soldiers, meaning 500 men who are at an age capable of fighting in the army, and three people die of disease in three days, then they can declare an official plague and observe a fast. If less people die then it is not a plague and they need not fast.
We should note that it is not clear if the law would be different if the city could produce 1,000 soldiers, or 10,000 soldiers. Would more people have to die in the same time period in order for it to be a plague? Can a plague be declared in a town with fewer people? These questions are not directly addressed by the mishnah.