Rif Eruvin 16a {Eruvin 55a continues ... 57a}

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16a

{Eruvin 55a continues}
Rav Huna said: A city constructed like a bow {like the letter C}, if there is between its two heads less than 4000 cubits, we measure from the extra {empty space}, and if there is between its two heads 4000 cubits, we measure from {the actual body of} the bow.

{Eruvin 55b}
"If the gedodiot {ruins} were {ten handbreadths} high":
What are gedodiot?
Rav Yehuda said: Three walls without a roof on top.

The Sages learnt {in a brayta}: These are they that are reckoned with it as its outskirts {from which we measure the techum}: A sepulchral monument which contains 4 X 4 cubits, and the bridge and cemetery which has a dwelling place in it, and a synagogue which has a dwelling place in it for the cantor, and a pagan temple which has a dwelling place for the priest, and horsestalls or storehouses in open fields to which dwelling places are attached, or watchmen's huts in a field, and a house on an island. These are reckoned with it as its outskirts. And the following are not reckoned with it as its outskirts. A sepulchral monument which is broken on two sides from one end to the other, a bridge or a cemetery that has no dwelling place in it, and a synagogue which has no dwelling place in it for the cantor, and a pagan temple which has no dwelling place for the priest, and horsestalls or storehouses in open fields to which dwelling places are not attached, a pit, a ditch, a cave, a wall, or a dove-cote in a field, and a house in a ship. These are not reckoned with it as its outskirts.

Rav Huna said: Those who dwell in huts measure {the techum} from their front door.
{Even if 100 huts are grouped together, they do not form a town.}

{Eruvin 56a}
The Sages learnt {in a brayta}: One who comes to square it should square it to the compass directions such that its north face should be to the world's North and the south face should be to the world's South. And your guiding marks are Ursa Major in the North and Scorpius to the South.

{Eruvin 57a}
Mishna:
A karpef {= area of 70 and 2/4 cubits} is given to the town. These are the words of Rabbi Meir. But the Sages say: They did not say karpef except between two towns; if this one has seventy amot and a fraction, and this one has seventy cubits and a fraction, he makes a karpef for the two of them to be as one.

And similarly three villages arranged in a triangle: if there are between the two outer ones 141 1/3, the middle one makes the three to be as one. {You imagine it moved down to occupy the middle space.}