When you break from the slog on the eastbound 10 this Thursday evening to swing by Leo’s for six or seven al pastor tacos (as one does) you may not know it, but you’re entering a religious district that’s hugely significant to practicing Jews.

This “eruv”—which includes Hancock Park, West Hollywood, Beverly Hills, Westwood, and Pico-Robertson, as well as parts of Sherman Oaks and Studio City—is walled off largely by the 10, 101, and 405 freeways. The spaces between those infrastructural boundaries are enclosed by 45 miles of fencing, walls, and, in some places, a thin wire stretched high overhead between utility poles. All of this ensures that 100 square miles of the city are ringed by a symbolic wall that is never broken by a gap wider than eight inches.

Screen capture courtesy Google Maps

The eruv functions as a communal domain for Orthodox Jews. According to Jewish law, certain acts of “work” are forbidden in public spaces on the sabbath—this includes carrying food or babies or books, as well as pushing strollers and wheelchairs.These actions get a pass within the private confines of the home or a communal domain. The eruv symbolically expands that private space to allow for, say, young families or wheelchair-bound elderly folks to get out of the house on Sabbath.

Eruvin exist in cities the world over, including New York and San Francisco (as well as the Valley). L.A.’s is the biggest in the country and, quite possibly, anywhere. Initiated by Howard Witkin (now the eruv’s executive director) when his wife was pregnant with their son, the Los Angeles Community Eruv took seven years to get up and running and was completed in 2002. It required lengthy consultation with both local government and religious experts in Israel.

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Eruv Society members did the physical work of constructing the walls and wires, and they currently maintain them with funds collected from local synagogues (about $120,000 annually). A team of three rabbis goes out every week—occasionally by helicopter—to check for sections downed by falling trees, wayward vehicles, or weather. Another team of Caltrans-authorized contractors drives out in a lift truck to make the needed repairs late on Thursday nights.

Those of us who aren’t practicing Jews pass in and out of the eruv and remain largely oblivious. Occasionally it surfaces in the news—as when construction on the 405 expansion in 2011 threatened the integrity of the eruv—but for the most part, the boundary markers exist out of sight and out of mind.

If you know where to look, though, they’re obvious. A wire runs between street lights along Western Avenue from the 10 up to Santa Monica Boulevard, for example. If you stand out front of the Wiltern and look west, you’ll see it on the opposite side of the intersection, about 20 feet up and surprisingly easy to spot. For most, the eruv is little more than especially fascinating trivia—a layering of significance on a city already rich with hidden gems. For many, though, it’s a requisite part of a weekly ritual, making religious practice and practical living compatible.

Thomas Harlander is a staff writer at Los Angeles magazine. You can follow him on Twitter and Instagram. He recently wrote: This Might Be the Best Argument for More Bike Lanes