Cities have layers of architecture and geography — streets, topography, buildings, utilities. There are metaphysical layers as well. In holy cities like Rome or Jerusalem, that spiritual layer receives top billing. But even in supposedly secular San Francisco, you can find it — if you know where to look.

Encompassing seven square miles of the city, the Richmond District eruv is one such layer, effectively invisible to most who traverse its boundaries. The eruv is an essential part of life for strictly Shabbat-observant Jews around the world; it is a boundary both physical and metaphysical that converts a public space to a communal one, allowing observant Jews to carry items — and, of great import to growing families, push strollers — within those bounds on Shabbat.

The Richmond eruv lies between Clement and Fulton streets north to south, and from 16th Avenue to 42nd Avenue east to west. It is overseen and maintained by Rabbi Shlomo Zarchi of Congregation Chevra Thilim, located within the eruv. It also encompasses the Schneerson Center, a Chabad outfit a few blocks away that serves mostly Russian speakers, and Congregation Anshey Sfard, a Sephardic synagogue on the edge of the eruv at 16th and Clement.

(There are two eruvs in San Francisco. The other one is in the Sunset District, centered around Orthodox synagogue Adath Israel. There is also one that encompasses parts of Berkeley and Albany and one in Palo Alto.)

Curious to know more, I set out with the rabbi on his weekly rounds as he checked the eruv. It must be checked before every Shabbat to make sure it is intact.

I often hear non-Orthodox Jews poke fun at the idea of an eruv. “A literal loophole in the law, just to make things easier,” a member of my Reform childhood synagogue once said to me with derision.

But that’s an unfair assessment that comes from a lack of understanding about a remarkably complex area of Jewish law. As Zarchi told me, the eruv is not a loophole but rather an elaboration of the law. It is no more a loophole than the halachic reasoning used to prevent capital punishment even though it is permitted by the Torah.

(After a few hours with Zarchi, I was honestly taken aback by the complexity of the issue. For a more thorough review, check out rabbikaganoff.com/an-eruv-primer.)

The boundaries of an eruv can be formed by two sorts of things: natural barriers such as a slope, a shoreline or the edge of a forest; and walls. For the purposes of an eruv, a wall can be composed entirely of doorways. From there, a doorway can be said to consist of its two posts and the top of the frame. And out of that interpretation comes the most common form of urban eruv: a line of telephone poles and the wires above, supplemented occasionally by pieces of string and the walls of existing buildings.

As we drove around the perimeter, Zarchi stopped several times to show me the particulars of his eruv. Like many urban eruvs, this one does not make use of any natural boundaries.

Where telephone wires run in a straight line between two poles, nothing needs to be done; in other places, a length of string connects two existing elements. In some places, a lechi, a kind of supplementary doorpost, is required to mark the end of one wall and the beginning of another as the eruv changes direction. Sometimes it’s simply a piece of string running down the side of a telephone pole. In one place we visited, the lechi was a length of wood affixed to the bottom of a pole and pointed straight up at wire overhead. How does Zarchi know it points directly up? He aligned it using a laser level, of course.

The eruv makes use of Comcast wires that run on PG&E poles. “Everyone plays a role in this mitzvah!” Zarchi quipped. Gaining permission from utility companies and neighborhood groups is often a major obstacle to creating an eruv. But in this case, it was a relatively smooth process. The Jewish Community Relations Council put Zarchi in touch with PG&E, which gave tacit approval.

A PG&E man went around with Zarchi once at the beginning to make sure everything was up to snuff. He slunk back to his car when a woman emerged from a house to accuse Zarchi of pirating cable; she had mistaken his eruv-building activities for something a tad more nefarious.

Things like that happen now and again. “I don’t want to make a scene,” Zarchi told me several times. In some cities, opposition to an eruv has focused on the perceived comingling of religion and state. But over a few lengths of string? That would be a stretch.

Although Zarchi grew up in Crown Heights, Brooklyn, where the Chabad rebbe prohibited the use of an eruv, his interest in establishing one here was sparked in part by his daughter’s impending birth four years ago. Without an eruv, neither he nor his wife would have been able to carry the baby to shul on Shabbat.

In the delivery room, in fact, Zarchi was on the phone troubleshooting with an eruv expert he’d brought in from out of town — so great was his commitment to getting the eruv up before his daughter was born. As soon as she was safely delivered, he was back in the streets working on the eruv.

Though the practical benefits of the eruv are key, Zarchi also touts its spiritual import. “Even if you don’t know it, you’re stepping through a door to serenity,” he said. “Before, you were just a person, but when you pass through into the eruv, you become part of a community.”

Eruv means literally “mixture” or “mingling,” which refers to the mingling of public and private domains created by an eruv.

To Zarchi’s surprise, this metaphorical communal space is important to a broader segment of the community than he expected. He recently received a question from an observant transgender Jew who sought the rabbi’s help in finding a place to live within the eruv. “When I started this, I didn’t know — who will use it? You can’t predict.”

Toward the end of our journey, explaining the location of the eruv’s eastern boundary on 16th Avenue, he said: “I could give you a whole Torah about why it goes down one street and not another.”

In many cities, the eruv costs a great deal to maintain. It can become a huge endeavor that encompasses wide swaths of terrain. Many cities in Israel are completely enclosed by an eruv. Zarchi’s is quite simple, humble even, and doesn’t require much upkeep. It’s limited, he said, “but you can always add to it later.”

Jew in the Pew is a regular feature. Send tips about religious, ritual and spiritual goings-on to [email protected].