Manhattan and the Modern City Eruv Question
The Manhattan eruv placed the full large-city question before the leading American poskim: millions of people and open public roads inside an island ringed by water, seawalls, bridges, tunnels, and substantial built structures. The debate concerned both the status of the city and whether those structures closed it according to halacha.
An island with many openings
The rivers around Manhattan could contribute to an enclosure, but the perimeter was pierced by bridges, tunnels, piers, shoreline access, and roads continuing into the rest of New York. Each crossing had to be reconciled with the proposed wall.
The Rebbe's letter to Rabbi Hertze Eisenstadt discusses Manhattan cautiously, asking how bridges, tunnels, tzuras hapesach, barriers, and toll structures affect the claim that the city is unquestionably a reshus harabim. The letter raises the points for examination; it does not issue a blanket heter.
Seawalls, barriers, and gates
Proposals relied at different times on seawalls, retaining structures, bridge equipment, and former toll barriers. A barrier used for traffic control is not automatically a halachic door: its position, width, ability to close the opening, and relation to the walls all matter.
Manhattan therefore possessed possible advantages that many inland cities lack, but also required a complete account of every public entrance through its natural boundary.
Rav Moshe did not permit the Manhattan eruv
In Orach Chaim I:138–139, Rav Moshe develops his early analysis of Manhattan as one city, its population, public roads, possible walls, and the consequence of visible carrying. He did not accept a practical eruv on the proposal before him.
When later proponents cited his nuanced language, Rav Moshe clarified his own position. In his letter to Rabbi Norman Lamm (4 Nissan 5724), he wrote that the Manhattan eruv was prohibited in his opinion and that his name must not be used as support. Orach Chaim IV:89 again says that he could neither permit nor assist it, while stopping short of denouncing qualified Rabbonim who ruled otherwise.
The public ruling against carrying
Agudath HaRabbonim issued a public prohibition against reliance on the Manhattan eruv (18 Sivan 5722). The surviving notice bears the names of Rav Aharon Kotler, Rav Yaakov Kamenetsky, Rav Gedalia Schorr, Rav Chaim Bick, and Rav Moshe Feinstein.
When the eruv was promoted again, the Union of Orthodox Rabbis reaffirmed the prohibition after a Chol Hamoed Pesach meeting attended by Rav Moshe (23 Nissan 5726). The practical public psak remained unchanged.
From Manhattan to other large cities
The later large-city proclamation of Kislev 5739 explicitly says that the Manhattan prohibition was not confined to the island and applied to New York and other large cities under the same halachic conditions.
That extension matters because Manhattan had unusually substantial possible boundaries. If those features did not produce an accepted public eruv, a neighborhood elsewhere in the metropolis could not rely on a lighter perimeter without confronting the same reshus-harabim and enclosure questions.