הנותן עירובו בבית הקברות אינו עירוב לפי שבית הקברות אסור בהנאה וכיון שרוצה בקיום העירוב שם אחר קנייה הרי נהנה בו ואם נתנו בבית הפרס הרי זה עירוב ואפי' היה כהן מפני שיכול להכניס שם במגדל הפורח או שינפח והולך:

Laws of where the eruv is placed. Contains 13 sections One who places his eruv in a cemetery — it is not a valid eruv, since a cemetery is forbidden in benefit, and since he wants the eruv to remain there after acquisition he is thereby benefiting from it. If he placed it in a beit hapras, it is a valid eruv, even for a priest, since he can enter there in a sealed chest or by blowing the ground as he walks.

The person and his eruv must be in the same domain so that it is possible for him to eat it during twilight. Therefore if he intended to spend Shabbat in a public domain and placed his eruv in a private domain, or intended to spend Shabbat in a private domain and placed his eruv in a public domain — it is not a valid eruv, since he cannot carry from a private domain to a public domain during twilight except through a transgression. But if he intended to spend Shabbat in a private domain or public domain and placed his eruv in a karmelit, or intended to spend Shabbat in a karmelit and placed his eruv in a private domain or public domain — it is a valid eruv, since during twilight when the eruv is acquired it is permitted to carry between either of those two domains and a karmelit for a matter of mitzva, as anything rabbinic was not decreed upon during twilight in a case of mitzva or pressing need.

If he placed it on top of a reed or giant reed growing from the ground — it is not a valid eruv, since being soft and easy to snap would make one liable for a sin-offering, and they decreed regarding them (and if they are as soft as a vegetable, see above at the beginning of Siman 336) even during twilight and even in a case of mitzva. If they were detached and stuck into the ground, it is a valid eruv.

If he placed it in a tower and locked it and the key was lost before Shabbat, or a rockslide fell upon it — if he can retrieve it without performing a biblically prohibited labor, it is a valid eruv.

Whoever places his eruv in a place has four cubits at the place of his eruv. Therefore one who places his eruv of boundaries at the end of his boundary and it rolled within four cubits — it is a valid eruv. If it rolled beyond four cubits, it is not a valid eruv.

If his eruv was lost, burned, or if it was at the end of the boundary and rolled beyond four cubits, or if it was terumah and became impure before nightfall — it is not a valid eruv. If it happened after nightfall — it is a valid eruv, since eruv acquisition occurs at twilight. If there is doubt, it is valid, as a doubtful eruv is valid — provided it had a presumption of validity, such as this case where he placed it there and a doubt arose. But if it had no presumption of validity — such as doubt whether it was placed there at all — no.

How is an eruv made? If one wishes to go to the end of the boundary or within it and let nightfall find him there — this is the primary way of fulfilling the mitzva. Even if he did not say "my Shabbat rest is in my place" but simply let nightfall find him there and said nothing — whether one who goes out from his house to let nightfall find him at the boundary, or one who was traveling and nightfall came upon him — he acquires two thousand cubits without any declaration. If he does not wish to trouble himself to be there at nightfall, he may go while it is still day and place there two meals' worth of food — each person according to his food requirement; if he is ill or a large eater, the measure is two average meals which is six eggs' worth of bread (see above Siman 368, section 3, or any food used for partnership of alleyways) — and if it is a relish, enough to eat with it two meals suffices. He then says "through this eruv I will be permitted to walk two thousand cubits tomorrow," and returns and sleeps in his house. Even so, his boundary is measured from the place of his eruv, since we consider him as if he lives there. But students who eat by householders whose homes are in the field and return to sleep in their teacher's house — their boundary is measured from their teacher's house, which is their sleeping place and their primary location, since that is where they would want to eat as well if their food were there.

If he wishes, he may send the eruv through an agent and say "through this eruv so-and-so shall be permitted to walk" — provided the agent is not deaf-mute, imbecile, or minor, or one who does not believe in the eruv. If he sent it through a deaf-mute, imbecile, minor, non-Jew, or one who does not believe in the eruv — it is not a valid eruv. But if he told another to receive it from the agent and sent it through one of these — even if he sent it by elephant or monkey and saw from a distance that it arrived and was given to the receiver — it is a valid eruv, even if he did not see the other person place it, since we presume an agent carries out his mission. Similarly, many who made a partnership eruv of boundaries and wished to send their eruv through another may do so.

If one person or many said to someone "go and make an eruv for us" and he made it for them in whichever direction he chose — it is a valid eruv and they may use it, since they did not specify a direction for him.

If one said to his fellow "make an eruv for me with dates" and he made it with dried figs; with dried figs and he made it with dates; "place my eruv in the tower" and he placed it in the dovecote; "in the dovecote" and he placed it in the tower; "in the house" and he placed it in the upper story; "in the upper story" and he placed it in the house — it is not a valid eruv. But if he said "make an eruv for me" without specification and he made it — whether with dried figs or dates, whether in the house or upper story — it is a valid eruv.

One who was traveling and recognized a tree or fence at the end of two thousand cubits and feared nightfall might come before he arrived there, and said "my Shabbat rest is beneath it at its base" — he acquires Shabbat rest at its base and has two thousand cubits from there, even if he cannot reach there before nightfall at a normal walking pace unless he runs. He is permitted to go there at a normal pace even if he does not arrive before nightfall. But if he could not reach there at all before nightfall, he may not move from his place, since he uprooted his intention from here and did not acquire there either. This applies specifically when he specified four cubits that are within two thousand cubits — such as saying "my Shabbat rest is at its base" and the distance from here to its base is no more than two thousand. But if the entire tree is not within two thousand cubits and he did not specify a place beneath it, he has not acquired Shabbat rest — since perhaps he had in mind four cubits that are beyond two thousand — and here too he has not acquired, since he uprooted his intention from here, and he may not move from his place. If the entire tree stands within two thousand cubits and he did not specify his Shabbat rest location — such as saying "my Shabbat rest is beneath it" — he has four thousand cubits from his location toward the tree, minus the measure of the tree's spread beneath it; for example if the tree's spread is twenty cubits, he has two thousand minus twenty cubits there. According to Rambam, one who acquires Shabbat rest at a distant place without specifying his Shabbat rest location has not acquired Shabbat rest there but only at the place where he was standing when nightfall came. Similarly if he said "my Shabbat rest is in such-and-such place" and it is more than two thousand cubits away, he acquires Shabbat rest at his own location. One who says "my Shabbat rest is beneath such-and-such tree" — if the area beneath it is eight cubits or more, he has not acquired Shabbat rest since he did not specify his Shabbat rest location; therefore he must intend to rest at its base or within four cubits to its north or south. If the area beneath it is less than eight cubits and he intended to rest beneath it, he has acquired Shabbat rest since his location is at least partially specified. The Rif rules similarly.

If there were two people, one who recognizes the place and one who does not — the one who does not recognize it entrusts his Shabbat rest to the one who does and says "our Shabbat rest is in such-and-such place."

This leniency was permitted only for a traveler, but not for one who is at home. If he said so, it does not count for him and he has only the Shabbat rest of his home.