Siman 408

Just as the sages instituted an eruv for courtyards and alleyways, so that they may carry in them by means of the eruv, because it makes it as if they all dwell in one place, so too they instituted eruvei techumin. This means that if one has a mitzvah need to go further than two thousand amot on Shabbat or some necessity—he can make an eruv on the eve of Shabbat for an additional two thousand amot, and he will be able to walk four thousand amot on Shabbat. This eruv is of two types: The first and primary one—on foot, which means that he goes on the eve of Shabbat while it is still day to the end of the two thousand amot, and sits there at the time of the acquisition of the residence, and says that it is his will that his residence be here, and automatically he has from this place two thousand in every direction. And he returns to his house and sleeps there, and nevertheless his residence is considered to be in the place where he was at the time of the acquisition of the residence. And the second—that the sages were lenient for the wealthy man, for whom it is a burden to acquire residence with his feet, that he may sit in his house and send by means of a messenger food for two meals to the end of the two thousand, and say that he acquires residence there. And the details of this matter will be explained in siman 409 with the help of Heaven.

Therefore, one who left the city on the eve of Shabbat and placed food for two meals far from the city within the techum, up until the end of the techum, and established his Shabbat dwelling there—even though he returned to his home while it was still day and slept in his home—nevertheless, we consider him as if he spent Shabbat in the location of the two meals, and he may walk from the place of his eruv two thousand amot in every direction. Therefore, when he walks two thousand amot toward the city, he only walks in the city until the end of his measurement. And if the city was swallowed within his measurement, the entire city is considered for him as four amot, and he completes his measurement to two thousand amot minus four amot outside of it.

How so? Behold, if one placed his eruv at a distance of one thousand amot from his house in the city to the east—it follows that on the next day he may walk two thousand amot to the east from the location of his eruv, and he may walk two thousand amot to the west from the location of his eruv: one thousand from the eruv until his house, and one thousand amot from his house within the city, and he may only walk in the city until the end of that thousand. And if from his house until the end of the city was less than a thousand, even by one amah or even less than that, such that his measurement concludes outside the city—the entire city is considered as four amot, and he may walk nine hundred and ninety-six amot outside of it to complete the two thousand. Therefore, if he placed his eruv at a distance of two thousand amot from his house in the city—he has lost the entire city, and it follows that he may walk two thousand amot from his house until his eruv, and he may not walk from his house in the city to the west even one amah. All of this is the opinion of the Rambam in chapter 6 of Eruvin, and our teacher, the Beit Yosef, ruled accordingly in section 1.

But the opinion of the Tur is not so, and he holds that even if his measurement ended in the middle of the city, and the city does not become like four amot for him—this is regarding the matter that they do not complete the remainder for him outside of the city. But nevertheless, regarding the matter that he may walk through all of it—it becomes like four amot for him, since he lodged in it. And specifically in a city that only by virtue of the measurement of the techum becomes like four amot, which is a city standing within two thousand and he did not lodge in it, for in that case we certainly say that when his measurement ends in the middle of the city—he has only half the city. But not in a city where he lodged, for if not so, the eruv would cause him a great stringency, for without the eruv it would have been considered as four amot, and the eruv was given to be lenient and not to be stringent, and our teacher, the Rema, agreed to this. And know, that which we said that when his measurement ends at the end of the city the entire city is like four amot—this is even if it ended before the ibbur, which is seventy amot, for we do not say the ibbur of the city is like the city itself to be stringent.

It has already been explained in siman 398 that the techumim of the city are measured in every direction two thousand amot with the filling of the corners, as is written there, and they measure the length to the east and to the west and likewise the width to the north and to the south according to the length of the city and according to its width, and this is opposite the city. And likewise, regarding one who places an eruv and they measure for him there two thousand for every direction—it is also opposite the place of the placement of the eruv, and consequently it is forbidden for him to go to the north and to the south, except opposite the width of the place in which he acquired shevitah and the corners. And if it is only four amot, such as when the eruv is not in a reshut hayachid enclosed for a dwelling—it is forbidden for him to go in any direction two thousand except opposite the four amot, and he fills their angles to make it a square tablet, as is written in siman 398.

In any event, our teacher, the Rema, wrote at the end of section 1, and this is his wording: "In any event, if the measure ends at the edge of the city and the whole [city] is like his four amot—it is permitted to walk its entire width, and he has two thousand [amot] outside the city to the north and to the south, even though he does not have such width opposite the place where he established an eruv." Thus far his words. And they wondered about him: what is the relevance of north and south to the city? The two thousand [amot] for every direction is opposite his place of dwelling and the corners that fill all the northern and southern two thousand [amot], and likewise in the east and west, but the city is not part of the measure of the techum at all. (This is the intent of the Magen Avraham, subsection 3). However, our teacher, the Rema, holds that since the city is considered as four amot—if so, it is also included within the techum, for behold, they deduct four amot from the techum because it is considered as four amot; if so, also opposite the city is like opposite the techum. (Avei HaOzer)

If opposite a portion of the city's width in any direction there is a city where the two thousand cubits end at the edge of the city, it becomes entirely like four cubits and the remainder is completed outside the city; and opposite the second portion of the width in this direction there is no city, or there is a city where its measurement ended in the middle of the city—we do not equalize the sides, but rather we follow here according to its measurement and there according to its measurement, and it is simple. (And so wrote the Sha'arei Teshuva in the name of the Noda BiYehuda). And one who places his eruv in a city, even a large one (like Nineveh), and even a ruined city or a cave fit for dwelling—he may walk through all of it and two thousand cubits outside of it in every direction. And one who places his eruv inside the city in which he spent the Shabbat—we do not measure from the place of his eruv, but rather he is like all the residents of the city, who have two thousand cubits in every direction outside the city. And so too if he placed his eruv in places that join to the city, such as houses standing within seventy cubits, or according to the opinion of the Tur within seventy cubits of the city—he has done nothing and he is like the residents of the city, for this is exactly like placing it in the city. And if he placed his eruv outside the techum—it is not an eruv, and he has the techum of his house. And we do not say that he uprooted his intention from his house, because such is his intention, that if the eruv is not effective—he should not lose the techum of his house, and it will be explained in siman 141. (See Magen Avraham subsection 4)