Work being done on the Southeast Denver Eruv.

What's The Point Of An Eruv?
 The Halacha of Eruvim.

— Prof. Adi Wyner

One of the 39 categories of prohibited activity on Shabbat is "carrying from one domain to the next" (hotzaah me-r'shut lir'shut). Jewish law prohibits carrying on Shabbat between a public domain and a private domain or for more than 4 cubits in a public domain. However, Halacha permits carrying within an enclosed private area.

Public domains are typically non-residential areas including streets, thoroughfares, plazas, highways, etc. Private domains are residential areas that can be deemed to be "closed off" from the surrounding public domains, such as individual homes or apartments that are surrounded by a wall. The Rabbis of the Talmud developed a means to render a larger area as a private domain by surrounding it with a structure that bears some similarity to a wall. Such an enclosure is called an Eruv; the more specific terminology is Eruv Chatzayrot or Shee-tu-fay M'vo'ot.

The Hebrew word Eruv means a "mixture" or "joining together" of separate entities into an integrated whole. When an Eruv is constructed around a defined geographical area, it integrates a number of private and public properties into one larger private domain. Consequently, observant Jewish individuals within an Eruv district are then permitted to carry objects within this area on Shabbat.

An Eruv signifies that this area is a community of people who consider themselves to belong to the same private domain.

An Eruv consists of constructions that are supposed to resemble a "door post" (tzurat ha-petach). The vertical parts of the "door posts" generally consist of telephone poles or other utility poles; the horizontal "lintel" part of the "door post" generally consists of strings connecting the poles to each other.

The string that serves as the lintel needs to be the lowest of the lines on the pole. If it is not, then it is necessary to string a new length of line between the affected set of poles. In addition, for a door post/lintel combination to be acceptable, the lintel must rest directly above the top of the doorposts. Note that this is not the typical way in which utility poles are constructed. Usually, the cable is attached to the side of the pole or to a structure that is held away from the pole. To address this issue, a thin rod may be attached to the pole to serve as the doorpost "surrogate" ("lechi"). In areas where the poles and lines do not exist, new pole/line combinations must be erected. These added poles must of course be high enough so as not to impede traffic. Fences may be used as part of the boundary without modification; however, if the ground is eroded beneath the fence to any significant degree, the space must be filled in. Lastly, all the areas to be enclosed must be "residential areas," or areas suitable for residential areas. It is not permitted to include cemeteries or bodies of water (such as lakes, streams, and ponds). Such areas must be excluded from the Eruv by enclosing them (either by not including them in the Eruv area, or by encircling them within the Eruv).

An Eruv is generally designed by encircling a community with a continuous string or wire. There are numerous regulations concerning the placement of this wire. Those who live in and use an Eruv have an obligation to ensure that the Eruv is intact before taking advantage of its presence. Usually, there is a group that maintains the Eruv that provides such information, and conducts weekly inspections.

Eruvim are most often found in communities where there is a critical mass of Jews who do not carry on Shabbat or who value Shabbat observance. Even people who do not observe all of the laws of Shabbat are generally supportive of an Eruv because it enhances Shabbat for those Jews that do observe the laws concerning carrying. In addition, the existence of an Eruv is essentially an affirmation of the existence of a Jewish community, consisting of Jews who are proud to express their collective Jewish identity. 

See article in this issue about the expansion of the Main Line Eruv.

Adi Wyner is Associate Professor of Statistics at University of Pennsylvania's Wharton School of Business. He is also "Rebbitzman" at Suburban JCC-B'nai Aaron. 


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