Chapter 5, Mishna 1, 2
Interesting coincidence: on the same day that I read about the need for zinc in order to stay healthy as we get older, and its primary source in food is meat, we encounter a dispute in our daf regarding the value of vegetables. The Sages believed strongly in the value of garlic and radishes, much less in other veggies. One also ages quicker in a city with too many ascents and descents. When squaring a city for the purposes of establishing its Shabbos boundary, we align it north and south. How did the ancients know the cardinal directions without a compass? Using the stars and the sun. They knew quite a bit about the motion of the heavens, even that a year is a few seconds less than 365 days and six hours. When are two cities that lie near each other regarded as one for purposes of the Shabbos boundary?