How do they make extensions for cities [for the purpose of defining the Shabbat limit]?If one house recedes and another projects, Or if one turret [of the wall] recedes and another projects, If there were ruins ten handbreadths high, or bridges, or sepulchral monuments that contained dwelling places, they extend the boundary of the town is to include them. And they make it [the Shabbat limit] like a square tablet in order that the use of the corners might be gained.

They give a karpaf [as an extension] for every town, the words of Rabbi Meir. But the sages say: they said [the of a] karpaf only in regard to two towns that if there was to this one [a piece] of land of seventy cubits and a fraction and to the other one [a piece of land] seventy cubits and a fraction, they can consider the karpaf as combining the two into one.

So also three villages arranged in the shape of a triangle, if between the two outer ones there is a distance of a hundred and forty-one and a third cubits, the middle one causes all the three of them to be regarded as one.

They measure the Shabbat limit only with a rope fifty cubits long, neither less nor more. And one should measure only while holding the end of the rope on a level with his heart. If he was measuring and he reached a valley or a wall he spans it and resumes his measuring. If he reached a hill he spans it and resumes his measuring, provided he does not go beyond the Shabbat limit. If he is unable to span it in connection with this Rabbi Dostai ben Yannai stated in the name of Rabbi Meir: “I have heard that they pierce the hills.”

They measure [the Shabbat limit] only through an expert. If he extended the limit at one point and limited it at another, they observe the place where he extended it. If there was one who made it a greater distance and one who made it a lesser distance, the greater distance is observed. Even a slave and even a female slave are believed when they say, “Thus far is the Shabbat limit”, since the sages did not enact the law in order to be strict but in order to be lenient.

If a town that belonged to an individual was converted into one belonging to the many, they may make an eruv for the entire town. But if a town belonged to the many and was converted into one belonging to an individual, they may not make an eruv for the entire town unless they excluded from it a section the size of the town of Hadashah in Judea, which contains fifty residents, the words of Rabbi Judah. Rabbi Shimon says: three courtyards each of which contains two houses.

If one was in the east and said to his son, “Prepare for me an eruv in the west”, or if he was in the west and he said to his son, “Prepare for me an eruv in the east”, if the distance between him and his house was no more than two thousand cubits and that between him and his eruv was more than this, he is permitted to go to his house but forbidden to go to his eruv. If the distance to his eruv was no more than two thousand cubits and that to his house more than this, he is forbidden to go to his house but permitted to go to his eruv. One who puts his eruv within the extension of a town, he has done nothing. If he put it even one cubit only beyond the limit he loses what he gains.

Rabbi Akiva said to them: Do you not agree with me that one who puts his eruv in a cave may walk no further than two thousand cubits from the place of his eruv? They replied: when is this true? Only where no people dwell in it, but where people dwell in it one may walk through the whole of it and two thousand cubits beyond it. Thus [where an eruv is put] within [the cave] the law is more lenient than [where one is put] on top of it. And to the measurer, of whom they spoke, they give him a distance of two thousand cubits even if the end of his measure terminates within a cave.