Yerushalayim, Visitors, and the Public Practice of Carrying
Yerushalayim occupies a distinctive place in the halachos of eruvin. It was a walled city with gates. It was also the city to which Yidden came from throughout Eretz Yisroel for the Regalim and for other obligations connected with the Beis Hamikdash. Those are two different features. The first concerns the physical status of the city. The second concerns what visitors would see and what they might learn from the public practice of carrying there.
Rav Moshe Feinstein used this second feature in discussing why Yerushalayim was left without an eruv, even according to an approach under which its physical enclosure could otherwise have made an eruv possible. He later returned to the same explanation and defined carefully how far the comparison could be carried.
Why would Yerushalayim have been left without an eruv?
In Igros Moshe, Orach Chaim I:139, Rav Moshe is discussing the proposed Manhattan eruv and the different ways the Rishonim understand a walled city and its public streets. In section 5 he reaches a difficulty. According to one reading of Rashi, Yerushalayim could have been capable of being joined by an eruv. If so, why was it not done?
Rav Moshe introduces his answer cautiously, with the words ולכן אולי, "therefore, perhaps." He writes:
Since people came to Yerushalayim from all places on the Regalim, and also throughout the year to bring korbanos and to eat maaser sheini, there was a concern that people from places that were not properly enclosed as Yerushalayim was would see people carrying there and would carry in those places as well. Therefore they did not make an eruv, so that carrying would remain forbidden in Yerushalayim too.
Rav Moshe is addressing habituation through visible communal practice. Someone who sees carrying permitted in Yerushalayim might return home without appreciating that the permission depended on physical conditions that did not exist there. The visitor's presence does not enter his discussion here as a change in residency or in the physical definition of a street.
The argument therefore concerns what people learn from public carrying. The separate questions of walls, gates, mefulash streets, width, shishim ribo, and the definition of reshus harabim still have to be decided on their own terms.
Rav Moshe's first comparison to Manhattan
In the same passage, Rav Moshe then applies the concern to Manhattan. He writes that Manhattan was a city to which people came from many places, including places nearby that could not be properly repaired for carrying. On the approach he was developing, he therefore saw a reason not to establish an eruv in Manhattan even if its own physical enclosure could otherwise be repaired.
This is one part of Rav Moshe's larger Manhattan discussion. His responsa address additional and independent questions concerning the city's physical boundaries, bridges, streets, walls, gates, and the status of a large public domain. Those issues belong in the full discussion of Rav Moshe's Manhattan responsa. The point here is narrower: Yerushalayim supplied Rav Moshe with a model for thinking about the effect of highly visible carrying in a city that draws people from far beyond its own neighborhoods.
The later qualification: which cities are comparable to Yerushalayim
Nearly three decades later, Rav Moshe returned to the same argument in Igros Moshe, Orach Chaim V:28. The later responsum is especially important because it prevents the Yerushalayim comparison from being turned into a rule about every large city.
After restating his explanation of why Yerushalayim was not joined by an eruv, Rav Moshe writes that this concern לא שייך בעיירות אחרות, "does not apply to other towns." Ordinary towns did not receive visitors from everywhere. Their visitors generally came from nearby places, so Rav Moshe says there was no reason on this account to prohibit an eruv there.
He then explains why he nevertheless treated New York differently:
It is not comparable to New York, concerning which I wrote that it appears proper to prohibit, because the reality now is that people come to New York from all over the world. This is only now, in our time, when even from distant places people come within a few hours by airplanes, and in a little more than a twenty-four-hour period there is almost no place from which they cannot come. Perhaps even by the railroads people came to New York from all the places and states in America, so that this concern could apply. But before that, it would not have applied even in New York, because it was not comparable to Yerushalayim, to which all of Israel necessarily came on the Regalim.
This qualification is unusually concrete. Rav Moshe does not treat the visitor concern as a timeless consequence of being a metropolis. He ties it to an actual pattern of travel. Air travel changed the practical reality of New York, and he even distinguishes the New York of his time from an earlier New York in which the same argument would not have applied.
Later in the same responsum he states the limitation again. The comparison with Yerushalayim cannot be extended to large cities generally; in the circumstances he was discussing, it applied to New York. He adds that the same consideration might extend to Brooklyn, provided there were no independent defect in its enclosure.
The reasoning is therefore fact-sensitive in both directions. A city does not acquire the Yerushalayim concern merely because it is large. At the same time, changes in transportation and the movement of people can create a practical situation that did not exist in an earlier generation.
The Old City and the new city are different physical questions
Yerushalayim also appears in a recorded discussion with the Rebbe for a different reason: the shape of its streets and the relationship between the Old City walls and the newer parts of the city.
During the yechidus of the Chief Rabbis of Eretz Yisroel on 26 Adar II 5746, Rabbi Mordechai Eliyahu discussed arrangements for the eruv in Yerushalayim. He spoke first about the Old City, its walls and gates, and the special arrangements there. Later he turned to the street layout of the new city. Its streets, he said, were not straight; they curved.
At that point the Rebbe interjected:
לא מפולש"Not mefulash."
Rabbi Eliyahu continued with the same point and then contrasted the curved streets of the newer city with gates of the Old City that stood in a direct line.
The exchange is useful because it keeps several concepts distinct. Walls and gates matter to the Old City's enclosure. The course of a street through the city raises the separate question of whether it is mefulash. A city may therefore present different halachic facts in different parts of the same municipality.
The speakers must also be kept distinct. Earlier in this same Yerushalayim exchange, Rabbi Eliyahu states his own view concerning shishim ribo and the existence of a reshus harabim in the present day. The Rebbe's clearly verifiable interjection in the street-layout discussion is the much narrower phrase לא מפולש. The recorded exchange is a discussion of Yerushalayim, not a recorded ruling about Crown Heights.
What the Yerushalayim comparison teaches
The two Yerushalayim discussions address different problems and meet at one important principle. An eruv is not decided by the name of a city alone.
Rav Moshe's visitor discussion asks who comes to the city, from where, and what public carrying there may teach them. His later responsum shows that the answer can change when patterns of travel change. The Chief Rabbis discussion asks how the actual streets run and how the old walled city differs from the newer city. Those facts can differ even within Yerushalayim itself.
For that reason, "Yerushalayim had an eruv" or "Yerushalayim did not have an eruv" is not, by itself, a usable rule for another city. One must identify which period, which part of the city, which physical enclosure, which streets, and which halachic question are being discussed. The same discipline is necessary when comparing Yerushalayim with New York, Brooklyn, or Crown Heights.