Rif Eruvin 16b {Eruvin 57a continues ... 58a}

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16b
{Eruvin 57a continues}
Gemara:
Rav Huna said: You give a karpaf to this one and a karpaf to that one.
Rabbi Chiyya bar Rav said: We only give a single karpaf to two cities.

We learn in Nedarim {56b}: One who takes a vow from a city is permitted to enter her techum but is forbidden to enter into her outskirts {all these things which extend the town before techum is measured}. How do we know that the outskirts of the city are reckoned as the city? Rabbi Yochanan said: For the verse states {Yehoshua 5:13}:

יג וַיְהִי, בִּהְיוֹת יְהוֹשֻׁעַ בִּירִיחוֹ, וַיִּשָּׂא עֵינָיו וַיַּרְא, וְהִנֵּה-אִישׁ עֹמֵד לְנֶגְדּוֹ וְחַרְבּוֹ שְׁלוּפָה בְּיָדוֹ; וַיֵּלֶךְ יְהוֹשֻׁעַ אֵלָיו וַיֹּאמֶר לוֹ, הֲלָנוּ אַתָּה אִם-לְצָרֵינוּ.

13 And it came to pass, when Joshua was by [literally "in"] Jericho, that he lifted up his eyes and looked, and, behold, there stood a man over against him with his sword drawn in his hand; and Joshua went unto him, and said unto him: 'Art thou for us, or for our adversaries?'

Now it could not mean that Yehoshua was actually in Yericho, for it is written (Yehoshua 6:1):

א וִירִיחוֹ סֹגֶרֶת וּמְסֻגֶּרֶת, מִפְּנֵי בְּנֵי יִשְׂרָאֵל: אֵין יוֹצֵא, וְאֵין בָּא.

1 Now Jericho was straitly shut up because of the children of Israel: none went out, and none came in.

Rather we deduce that he was in its outskirts.

{Eruvin 57b}
Mishna:
One may measure only with a rope of fifty cubits, not less and not more. And one may not measure except opposite his heart.
If he was measuring and he reached a valley or a fence, he absorbs it {=does not measure the incline but rather only the horizontal} and he returns to his measure.
If he reached a hill, he absorbs it and he returns to his measure,
{Eruvin 58a}
provided that he does not go out beyond the bounds.
If he is not able to absorb it {since the width of the valley or hill exceeds 50 cubits}, regarding this Rabbi Dostai the son of Rabbi Yannai cited Rabbi Meir: I heard that they cut through in the hills.

Gemara:
"not less and not more":
One taught: Not less {than a 50 cubit rope} because it increases the measure {since the rope will be stretched}, and not more because it decreases the measure {since the rope cannot be stretched out enough}.

Rav Yosef learned: There are three types of rope. Of megeg {= a type of reed}, of wicker, and of flax. The megeg was used for the ref heifer {para aduma}, for we learned in the Mishna {in Para}: They bound it with a rope of megeg and put it on its pile. Of wicker for a suspected adulteress, for we learn in a Mishna: And after that he brings a wicker rope. And of flax for measuring {techum}.

"If he was measuring and he reached a valley or a fence":
From that which it states "he returns to his measure," this implies that if he is unable to span it {since it is more than 50 cubits across}, he proceeds to a position from which he is able to span it, and spans it, making the necessary observations {such that he can locate the point on the far side," and then returns {to the opposite side of the valley}.

Thus we have learnt what the Rabbis have taught elsewhere: For the Sages learnt {in a brayta}: If he was measuring and reached a valley, if he is able to absorb it with a rope of 50 cubits, he absorbs {=spans over} it. And if not, he walks to a place where he is able to absorb it, and spans it, making the necessary observations, and returns to his measuring. And if the valley was crooked {i.e. its narrow section (which is < style="font-style: italic;">techum was being measured}, it is "pierced" in an upward direction and "pierced" in a downward direction. If he reaches a wall, we do not say that the wall must be bored through. Rather we estimate its width and continue measuring {from its opposite side}.

However, if it easy to make use of the wall {since it gently slopes upwards}, he conducts a firm measuring of it.

Rav Yehuda cited Shmuel: They only learned this regarding a plumb line will not descend in a straight line {to the floor of the valley, because of the slope}.