עירובין ה׳:ג׳ - ה׳:ד׳

וכן שלשה כפרים משולשים – on actually a triangle, but the third stands from afar corresponding to between the outer ones (i.e., towns) , and everything, for whereas, the middle [town] enters between them and there isn’t anything between this one and that one other than one-hundred and forty one and one-third cubits , which are seventy cubits and two-thirds [of a cubit] to this one, and seventy and two-thirds [of a cubit] to that one, and similarly, to the side of the other outer city/town. There is nothing between the middle one (i.e., town/city) and it other than one-hundred and forty-one cubits and one-third [of a cubit], all three of them (i.e., the towns/cities) are thought of as one [city/town]. But the person who leaves from one of them to to go through its neighbor counts from the wall of its outer neighbor. And how much should there be between the middle [city/town] to the outer [city/town]? Two-thousand cubits, for since the middle [town/city] is capable of going to the outer one and outer one to the middle one without an Eruv, we state that we see it as if the middle one is placed between them. But if it is further than two-thousand [cubits], we don’t say that we see it.

אין מודדין – two-thousand cubits of the Sabbath limit other than with a flax rope that is fifty cubits long.

לא פחות – that if the rope is short, it is greatly stretched and lengthens [one must say, the measurement].

ולא יותר – when it is too long, it becomes heavy, he doubles it at its middle and shortens it.

אלא כנגד לבו (at level with his heart) – The Sages established for him a place to put the head of the rope, every person level with his heart, for if this person would place it corresponding to his neck and the other corresponding to his feet, the rope would shorten and the [Sabbath] limits would grow shorter.

מבליעו (takes account only of the horizontal span/includes it) – if it is not fifty cubit wide from border to border from above, even though there is in its sloping going more than one-thousand, we don’t say that he should raise the measurement of his slope to the measurement of the [Sabbath] limit, but rather, this should stand on the border from here, and that should stand on its border from there and absorb (i.e., include) it from the slope with one rope.

וחוזר למדתו – for since it teaches, “continues his measuring” – implying that if its width that corresponded to the town/city was more than fifty [cubits] and he was not able to absorb it/include it there with the rope, and with one of its heads that does not correspond to the town/city, he can absorb it/include it there, and measure and go there from the border and beyond until it corresponds to the place where the the width of the valley ends sin it corresponding to he city/town, and he returns to his measurement corresponding to the town/city and completes the measurement of its [Sabbath] limits.

הגיע להר מבליעו – and this is so that the mountain/hill will not be standing upright a great deal, but rather slanting, for in the walking of five cubits from it, he will not raise it (i.e., the rope) other than ten handbreadths, if it is standing straight up until with at least of the distance of five cubits it is standing upright ten handbreadths, he doesn’t include it/absorb it, but rather, estimates it alone and goes on.

והוא שלא יצא חוץ לתחום – when he measurer goes to include the hill/mountain or the valley, he should not leave outside of the [Sabbath] limit to a a place where the tops of the valley are short – that he is able to absorb them there in order that he can return afterwards to his measurement corresponding to the town/city, as a decree, because a person who sees it measures it and goes there would say that the measurement of the [Sabbath] limit of the sides of the city/town come up to here.

בזו אמר רבי דוסתאי – with this, to exclude the city of refuge and the heifer whose neck is broken that is nearest to the space/cavity that they don’t estimate the level distance between two places separated by mountains (see Talmud Eruvin 58a-b – because they are from the Written Torah).

מקדרין – they perforate, they see as if they perforate them and measure the path of the perforation, to exclude the measurement of its sloping, as we stated in the Gemara (Tractate Eruvin 58b) that they measure it with a rope of four cubits and the bottom they place the rope corresponding to his heart and at the top corresponding to his feet, and similarly they measure it all four cubits by four cubits and they deduct the slope of all four cubits by half the height of a person. And the Halakha is according to Rabbi Dostai.