Gemara

R. Yehoshua: Once, a girl outwitted me. I was walking on a road that went through a field. She said 'Rebbi, isn't this a field?'

R. Yehoshua: It has already been trodden [through many people]!

The girl: Robbers like you trampled it!

Bava Basra 12a (R. Yochanan): If Mavo'os open to a road leading to another city, and people of this city want to close them, people of the other city can stop them;

(Rav Yehudah): If Rabim became Muchzak in a path, one may not ruin it.

60b (R. Yakov): If one recessed his house from Reshus ha'Rabim, R. Yochanan forbids him to return the walls until the original border, like Rav Yehudah's law;

Reish Lakish permits. He holds that Rav Yehudah's law does not apply here, for enough room for people will remain [like before he recessed].

99b (Mishnah): If a Reshus ha'Rabim passed through Reuven's field, and Reuven took it and gave to them a path on the side, they acquired what he gave, but he did not acquire his [desire, i.e. the old path].

Question: Why doesn't Reuven get it? He should be allowed to take a stick and hit anyone who walks there!

Answer: This teaches that one may not take the law into his own hands.

Rejection #1 (Rav Zvid): Chachamim decreed that he does not get it, lest he give a crooked path in its stead.

Answer #2 (Rav Mesharshiya): The case is, he gave them a crooked path in its stead.

Answer #3 (Rav Ashi): Any replacement path he gives is considered crooked, for it is closer for some people, but further for others.

Question: If so, why does he lose the path he gave? Let him say 'take your path, and return mine!'

Answer: Our Mishnah is R. Eliezer;

(Beraisa - R. Eliezer): If the public chose a path [in Reuven's property], they keep it.

(Rav Gidal citing Rav): The case is, they had a path in Reuven's land, and it was lost.

Rabah bar Rav Huna said that Rav rules like unlike R. Eliezer. He explains our Mishnah like Rav Yehudah's law [above].

According to R. Eliezer, the public acquire the path through walking on it.

(R. Yosi b'Rebbi Chanina): Chachamim admit to R. Eliezer about a path in a vineyard. Since it is exclusively for walking, it is acquired through walking.

Rishonim

Rambam (Hilchos Nizkei Mamon 13:24): If one recessed his property from Reshus ha'Rabim, he may never return the walls, for one may not ruin a path in which the public was Machazik.

Rashba (1152): What is the Chazakah of a Rabim in a path, after which one may not ruin it? It is after many walk through it, like in Bava Basra. R. Eliezer holds that they acquired through walking. Also on 12a, the Gemara connotes like this. However, 60b connotes that they acquire once it is opened for the Rabim, even before they go through it! R. Yochanan forbids returning the walls even before the Rabim were Muchzak to go there. If not, the Gemara should have said that they argue about returning after the Rabim became Muchzak! This shows that the same applies after they were Muchzak. Stam, people do not refrain from passing through [when they are able to]. Similarly, if a Chatzer was breached to Reshus ha'Rabim, R. Eliezer obligates one who throws from the Chatzer to Reshus ha'Yachid (Eruvin 94a). The Gemara says that this is like he holds, that once the Rabim chose a path they keep it. Even though R. Eliezer's law depends on choosing a path and Chazakah through walking, it was taught Stam, and did not say that there was a Chazakah through walking.

Nimukei Yosef (49a DH Gemara): The questioner thought that letter of the law, Reuven should acquire the old path, for he benefits and the Rabim do not lose, so Kofin Al Midas Sedom. (We force one to let others benefit, if he will not lose.) Reuven does not get it, for one cannot take the Rabim to a judgment. Therefore, we asked that he should take the law into his own hands. One may do so when needed to avoid a loss. He does not even get back the path he gave, due to Rav Yehudah's law. The Ramah says that this is only after they were Machazik with the owner's consent. This is even if he erred, like here. Rav Ashi answered that letter of the law, he does not receive the old path, for surely it is longer for some people. Rabanan fined him, for they are adamant about damage to the Rabim.

Tosfos (12a DH Metzar): If Rabim became Muchzak in a path with Reshus, one may not ruin it. If they seek to be Machazik without Reshus, one may take a stick and protest against them (Bava Kama 28a. It cites most of the Sugya in Bava Basra 99b - PF.)

Rashi (Bava Kama 28a DH Iy): If the new path is not a good replacement, why doesn't he get the old path?

Tosfos (Bava Kama 28a DH Iy): The text of the Gemara does not say 'if so, why doesn't he receive the old path'?

R. Shimshon (Ohalos 18:4): A field in which people cry over Mesim gets this status because the owner despairs (Mo'ed Katan 5b). This is like Rabim who became Muchzak in a path. One may not ruin it. If the owner did not despair, the Rabim were Machazik improperly, so one may ruin it.

Gra (CM 377 Likut): Rashi in Mo'ed Katan explained differently, for he holds that if Rabim became Muchzak in a path even without Reshus, one may not ruin it, like he said in Bava Kama. However, Rashi is very difficult.

Poskim

Shulchan Aruch (CM 377:1): If a Reshus ha'Rabim passed through Reuven's field, and Reuven took it and gave to them a path on the side, they acquired what he gave, but he did not acquire what he took.

SMA (1): It seems that the Rabim acquire both paths only if anyone who wants to go there, even from other places, goes there. Reuven cannot be Mevatel their rights to the old path, and they acquired the new path with his consent. If the path was only for people of a Mavoy, or of one city, the people of that city, or even the seven governors of the city, can switch it for another path. No one can protest. Their actions are binding. All the more so, the Rabim do not acquire both paths.

Be'er ha'Golah (3): The Rambam concluded (13:27) 'Reshus ha'Rabim must be at least 16 Amos wide.' Why did the Mechaber omit this?

Pischei Teshuvah (1): Be'er ha'Golah understood that the Rambam's final words (13:27) explain his former words (13:24); also the Rema's law applies only to a path 16 Amos wide. Teshuvas Pnei Yehoshua (1 CM 4) says that the simple reading of the Rambam in Hilchos Nizkei Mamon connotes like this, but this is wrong. We bring Rav Yehudah's law regarding a Mavoy, even though a Stam Mavoy is not so wide. Also, none of the Poskim bring this. The Rashbam (100a DH she'Hechziku) says that the Rabim leveled and fixed the path to walk on it. This implies that walking is not enough. Perhaps a Mavoy is different, for it is made to walk in. This is its use, therefore it is acquired through walking, just like a path in a vineyard. Everything is acquired through its normal use. Also, all the Poskim wrote Stam, and did not require a real Chazakah. Also, perhaps the Rashbam teaches that [alternatively,] they [can] acquire through fixing the path, even before walking on it.

Rema: If Rabim became Muchzak in a path with Reshus, one may not ruin it.

Beis Yosef (DH Mi): The Rashba explains that 'Rabim became Muchzak in a path' means that they leveled it and fixed it to go on it, and the owner knew and was silent. Surely, he pardoned them, and all the more so in our Mishnah, in which he himself gave a path to them. Therefore, he cannot retract, i.e. if they were Machazik in it.

SMA (2): If they were Machazik without Reshus, one may ruin it. However, if we see the Rabim Muchzak in a path, we claim for them that surely, they were Machazik with Reshus.

Gra (Likut): This is only with Reshus. We learn from Bava Kama 28a. Rav Yehudah's law explains why he cannot take back the new path, but not why he does not get the old path, like Tosfos (28a) says. I do not understand Rashi there.

Note: Mahadura Basra (Bava Kama 28a) says that Rashi had the text Tosfos rejected, and explains that it means that he does not get back the path that he gave.

Pischei Teshuvah (2): A case occurred in which Shimon's wall slanted away from Reshus ha'Rabim. He says that it was initially straight, and wants to make it straight again. The Rabim have enough room. Reuven says that it was always slanted, and the path will be less spacious if the wall is straight. Teshuvas ha'Rashba (3:156) rules like Reuven. We hold like R. Yochanan (417:2), who forbids one who recessed to return to his former boundary, for this narrows Reshus ha'Rabim, even if it is 16 Amos wide. Shimon must prove that the wall slanted afterwards. Beis Efrayim (CM 22) learns from here that even if one recessed only one corner, he may not return it later. However, perhaps this is only if he willingly gave it with intent that they use it permanently. Surely this does not apply to a corner. He merely left it free until he will need it. It is as if he lent the area to the Rabim. They were Machazik without Reshus. People often leave an empty area, and people walk on it, and they take it back afterwards. This is unlike one who built on his property and left free space. He intended to let the Rabim walk there. There is no proof from the Rashba. Reuven says that Shimon never recessed!

Pischei Teshuvah (3): The Rema (162:1) forbids putting doors on a Mavoy from this reason, unless the king gave Reshus. I say that l'Chatchilah, one may not ask Reshus for this.