During the latter part of the 17th century, when Jews were allowed to move outside those streets, cities had outgrown their walls and newer cities were built without walls altogether. For the purpose of eruvin it was no longer a given that cities were closed and therefore mechitzos had to be constructed. It was obviously easier to use natural walls that circumscribed entire cities, such as riverbanks and canals, than to erect tzuras hapesachim, which would have required permission from the civil authorities. Teshuvos written at that time addressed the possibility of utilizing canals and rivers as the necessary walls to enclose cities such as The Hague (Chacham Tzvi, siman 5 and Ohel Yaakov, siman 73) and Rotterdam (Shev Yaakov, siman 17 and Shvus Yaakov, 3:28). During the latter part of the 19th century, as telegraph, telephone, and electric wires sprung up all over the countryside, they were incorporated into the community eruv as well (Eitz HaChaim, siman 246-249; Maamer Mordechai, siman 31, and Nefesh Chayah, siman 34).
Prior to World War II almost all cities with Jewish populations established eruvin including Vilna (Mishmeres Sholom, 24:10) and Radin (Dugmah M’Darchei Avi, p. 31). In the times of Rav Shmuel Salant zt”l tens of thousands of people utilized the eruv and carried in Yerushalayim on Shabbos (Chazon Ish O.C. 39:5). Even the following large cities with populations of 600,000 erected eruvin: Warsaw (Mishmeres Sholom, 24:10; Divrei Menachem, O.C. vol. 2, pp. 42-43, and Rocznik Statystyczny Warszawy 1921 i 1922, 1924 p. 14), Lodz (Mishmeres Sholom, 24:10 and Encyclopedia Judaica, 1996 vol. 11 p. 426), Odessa (Divrei Malkiel, 3:14-18, 4:3; Tikkun Shabbos, and Tuv Yehoshua), Manchester (introduction Bais Av vol. 2 and Encyclopedia Britannica, 1911 vol. 17 p. 547), St. Louis (Tikvas Zechariah and Encyclopedia Britannica, 1911 vol. 24 p. 24), and New York in 1905 (Oznei Yehoshua, 1:18; Tirosh VaYitzhar, siman 73; Eruv V’Hotzaah, and US Census, 1900).
In order to satisfy the civil authorities and remain inconspicuous, the eruvin of our grandparents’ time relied on existing enclosures such as riverbanks and telegraph wires. As a result of the circumstances under which these eruvin were constructed, the poskim usually permitted major leniencies. As is evident from nearly all the teshuvos written about eruvin prior to World War II, the question then was not whether an eruv was permissible, only how to construct one. Just as it was the responsibility of each rav to insure that there be a kosher mikveh in his community it was incumbent on each rav to erect an eruv as well (Teshuvos V’Hanhagos, 1:844; see also Chasam Sofer, O.C. 99). If the rav of the city did not erect an eruv, it was not for the lack of effort; the civil authorities did not permit the construction of one.
Today we are fortunate that we can erect our own tzuras hapesachim and to construct eruvin that are far superior to the ones that were erected in the preceding era.