Unbeknownst to many, there are translucent fishing lines that wrap around hundreds of cities around the world. Strung high above the heads of pedestrians and roofs of houses, on utility poles and lamp posts, these wires are barely visible and hardly affect the lives of millions that live in these cities. But for the orthodox Jews, these imperceptible wires that run for dozens of miles, mark an important religious boundary that allow the devoted to hold on to their faith.

The wires mark the boundary of a ritualistic enclosure called an eruv, within which observant Jews can perform certain duties that they are not allowed to outside of home, during Sabbath. These duties are often mundane, like carrying house keys, tissues, medicines, or using strollers to push babies around, but essential enough to function in life. Following the rules of Sabbath, hence, not only interferes with life but also prevents Jews from fulfilling their religious duties. For instance, families with small children, who use prams and pushchairs, or the physically disabled, who use wheelchairs, are effectively housebound. They can't even go to the synagogue.

A section of an eruv in Manhattan, New York. Photo credit: New York Post

So Jews hang wires around their neighborhood to create an enclosed space, because according to Jewish law, an enclosed space is considered a private domain. Within this private domain —the eruv— Orthodox Jews can carry objects or push prams or wheelchairs, or otherwise follow the same rules on Sabbath that they would in their homes.

In ancient times, eruvs were closed courtyards containing several Jewish homes and often a synagogue. Sometimes physical boundaries such as walls, hedges, and roads were considered to enclose an area of land. Many communities in the past, and entire cities were walled, making it possible for observers to carry on, on Shabbat, since one is never leaving one's domain.

As communities grew large, it became impossible to contain them within walls. So they started erecting poles and strung wires to enclose an area, because for all intents and purposes, a piece of string is as good as a wall. How? Well, a wall can be a wall even if it has many doorways creating large open spaces, which means that a wall does not have to be solid. So two poles with a string across can be taken as a doorway in the boundary. The entire “wall” is therefore a series of “doorways”.

Eruvs are everywhere, from Melbourne to Manhattan, from Toronto to Tel Aviv. They are regularly checked to ensure their integrity. Organizations who carry these checks and perform repairs have either a telephone number or a website where anyone can check whether the eruv is in working order. The cost of upkeep of an eruv in often born by synagogues in the area. In cities as large as New York, for instance, this can amount to a tidy sum.

There has also been all sorts of controversies centered around the construction of eruvs. Jewish communities have to seek permission from the city municipality or council before erecting a eruv. Sometimes these are refused. Then, even within the observant community, there are some who believe that eruvs are just loopholes that the rabbis devised to get around the prohibition against carrying on Sabbath, and question the legitimacy of these flimsy boundaries.

Map of eruvs around Brooklyn, New York.

Map of the Manhattan eruv.

Map of the eruv in Amsterdam.

A section of an eruv in Manhattan, New York. Photo credit: New York Post

The string of an eruv in Ventura Boulevard in Los Angeles. Photo credit: waltarrrrr/Flickr

The string of Los Angles Community Eruv runs over a utility pole. Photo credit: waltarrrrr/Flickr

The string of an eruv visible against the blue sky in Lincoln Square, New York. Photo credit: Billie Grace Ward/Flickr

A man attaching a wire t a light pole to create an eruv in Malden, Massachusetts, United States. Photo credit: www.bostonglobe.com

A plastic string of an eruv runs over a neighborhood in Malden, Massachusetts, United States. Photo credit: www.bostonglobe.com

The string of an eruv in New York City. Photo credit: Ella/Flickr

Sources: Wikipedia / Chabad.org / BBC / Jewcy.com