Exterior Walls and Omed Merube in Crown Heights

The proposed Crown Heights eruv is described as relying on more than poles and wires. Its published English description says that the enclosure is omed merube al haparutz, with "80% walls." The Hebrew description is stronger, calling them "eighty percent complete walls made by man."

That description places the exterior physical boundary at the center of the halachic question. Genuine walls can have a force that an ordinary tzuras hapesach does not have. An urban area surrounded by valid mechitzos therefore has to be examined according to the actual walls that form its perimeter, the openings through those walls, and the way each opening is treated.

For Crown Heights, the proposed exterior boundary reaches well beyond the neighborhood itself. Building faces, fences, retaining walls, slopes, highway structures and rail structures can each have a different halachic status. Bridges, underpasses, ramps, streets, gates and gaps can interrupt an otherwise substantial wall. A percentage is meaningful only after those physical features have been identified and measured according to their halachic status.

What does "80 percent walls" mean?

The basic rule of omed merube appears explicitly in the Alter Rebbe's Shulchan Aruch, Orach Chaim 362:18:

Any enclosure of walls in which the open portion is greater than the standing portion is forbidden and is regarded as entirely open, unless each individual breach is less than three tefachim. If the open portion and the standing portion are exactly equal, it is permitted, because the halacha requires that the majority not be open; it does not require a majority of standing wall, provided that no single opening is greater than ten amos. An opening up to ten amos, inclusive, is permitted because it is regarded as a doorway.

A percentage calculation therefore begins with the halachic enclosure itself. "Eighty percent walls" requires a denominator: the measured length of the perimeter being evaluated. It also requires a numerator: the measured portions of that perimeter that qualify as standing wall.

The calculation changes wherever the physical boundary changes. A building face may be wall while the street beside or between buildings is an opening. A retaining wall ends where a driveway cuts through it. A steep embankment counts only along the stretch where its dimensions qualify as a mechitza. Gates, missing fence panels, road crossings and changes of grade each affect the length that can be counted as standing wall.

The published eighty-percent figure is given without a measured total perimeter, a measured total of qualifying wall, a segment-by-segment wall schedule, a stated measurement method, or a survey date. The published material also gives no calculation showing which kinds of structures were included in the wall total and how gaps or public crossings were deducted. The figure therefore cannot presently be reproduced from the published information.

Even a fully documented aggregate calculation would leave individual openings to be addressed. The Alter Rebbe's rule of omed merube immediately adds that a single opening greater than ten amos has its own status. The next se'if discusses the use of a tzuras hapesach at such an opening and records a stringent opinion as well. The total wall percentage and the validity of each major opening are therefore separate parts of the enclosure analysis.

What may count as a wall?

A city perimeter may combine several kinds of mechitzos. Each stretch depends on the physical form, dimensions and continuity present at that location.

Buildings and continuous building lines

An actual building wall can serve as a physical wall. A continuous line of structures can therefore contribute substantially to an enclosure. Streets that cut between those structures remain openings in the line and require their own halachic treatment.

This distinction is central to Rav Moshe Feinstein's discussion in Igros Moshe, Orach Chaim V:28. Rav Moshe addresses the view that the built portions of a large city can constitute omed merube against the streets crossing between them. He explains:

It cannot be said that the minority open portion, when the standing portion is greater, is considered actually fenced in practice to the extent that it cancels the passage of the public. The place is open in reality and the public passes through it. The law of omed merube al haparutz means only that when the standing portion is greater around the enclosure, the entire place is considered enclosed. It does not mean that the open place is regarded in reality as fenced.

Rav Moshe continues that omed merube applies to an ordinary breach. It cannot be used "to contradict what is evident" by treating a way made for public passage as though a physical wall closes it.

For a Brooklyn perimeter that relies on building fronts, the building walls may enter the standing-wall calculation. The street cutting through that line still retains its own status. Its width, use and halachic treatment have to be determined separately.

Fences, retaining walls and constructed barriers

A substantial fence, retaining wall, parapet or other constructed barrier may constitute a mechitza where it has the required halachic height and continuity. The Alter Rebbe also recognizes the physical status of a qualifying wall even when it was originally built for another purpose.

Only the qualifying stretch enters the wall calculation. A gate, driveway, access road, missing section or reduction in height can create an opening. A highway concrete barrier may run continuously for one stretch and terminate at an interchange. A rail fence may extend for a considerable distance and open at a street, station entrance or service access. Each transition changes the physical boundary being measured.

A broad category such as "highway wall" or "railroad wall" therefore supplies too little information for the percentage. The actual structure and every interruption along the claimed perimeter have to be known.

Slopes and tel hamislaket

A sufficiently steep slope can itself have the halachic force of a wall. The classic measure is a rise of ten tefachim within four amos. The Alter Rebbe describes both a riverbank and a dry-land slope with that rise as a mechitza.

The dimensions must exist along the stretch being counted. An embankment can be steep enough in one place and too gradual farther along. Modern grading can introduce driveways, ramps and paths through a slope. A perimeter that relies on a tel hamislaket therefore requires actual measurements along the route.

Orach Chaim 363 also discusses the effect of substantial public passage over a tel used as a mechitza. That adds a separate question wherever a perimeter relies on a slope traversed by the public. The current Hebrew description of the proposed boundary specifically calls the claimed walls "complete walls made by man," so the calculation should identify which segments are being counted in that category and how their openings are treated.

Gud asik and a wall below the level of travel

Gud asik is the principle by which a qualifying wall below can, in the proper circumstances, be regarded as continuing upward. It becomes relevant when a shoreline wall, retaining wall or other boundary lies below the surface that needs enclosure.

Its application depends on the actual wall and its relationship to the level above. A vertical structure somewhere below a road does not by itself establish a continuous wall through the road surface.

Rabbi Sholom Dovber Levin applies this issue to large-city eruvin in his discussion of bridges. When a riverbank or embankment serves as a wall and a bridge carries a public road across it, the road crosses the line of the claimed mechitza. His discussion, citing the Tzemach Tzedek and the Alter Rebbe, addresses the limits of gud asik where the lower wall is unrecognizable at the upper level or public passage cuts through the boundary.

The bridge opening therefore requires its own treatment even when valid wall continues on both sides of it.

Gud achis, pi tikra and elevated structures

Gud achis treats a qualifying boundary above as descending downward. A related principle, pi tikra yored vesosem, can treat the edge of a roof as descending and closing the space beneath it in circumstances defined by halacha.

Elevated railways, bridge decks and overpasses still require an analysis of the particular structure and the public passage beneath it.

Rav Moshe addressed such a proposal in Igros Moshe, Orach Chaim I:139. A proposed Brooklyn enclosure sought to use the elevated railway as one of its physical boundaries by treating the edge of the structure as a descending wall. Rav Moshe examines pi tikra, gud achis and public passage at length. He rejects the proposed use of that elevated structure as the wall required for the public domain beneath it. Among the considerations he discusses are the purpose for which the structure was made and the fact that the space beneath it was made for public passage.

The same distinctions matter in Crown Heights. A retaining wall beside a railway, an elevated track on columns, a solid bridge abutment and the open space beneath an overpass are four different physical conditions. Each has to be classified according to the mechitza actually present there before its length can be included in a wall total.

Openings greater than ten amos

The ten-amah rule prevents the wall calculation from ending with a single percentage.

Consider a perimeter made of eighty feet of valid wall and twenty feet of open space. The arithmetic gives eighty percent standing wall. If the entire twenty-foot opening forms one large breach, halacha still requires that opening to be addressed under the laws governing a breach greater than ten amos.

A valid tzuras hapesach can in many circumstances give an opening the form of a doorway. The Alter Rebbe discusses this immediately after the law of omed merube. He also records a stringent view concerning a tzuras hapesach over a breach greater than ten amos unless the required standing wall remains greater. The complete rules belong to the general halachos of enclosure. For the Crown Heights exterior boundary, the practical requirement is clear: the wall calculation has to identify the major openings and the halachic correction relied upon at each one.

A continuous line drawn across a street, ramp or entrance on a map gives no answer by itself. That location may be physical wall, a permissible opening, an opening repaired by tzuras hapesach, or a breach requiring some other treatment.

Sixteen-amah streets and public breaches

Sixteen amos is the classic width associated with a reshus harabim. The status of a particular Brooklyn street depends on the full set of relevant conditions, which are treated elsewhere. When a broad public street cuts through a proposed line of building walls, however, the street has to be analyzed as a public opening in the perimeter.

Rav Moshe addresses this point directly in Orach Chaim V:28. The discussion concerns intersecting city streets and a theory that the greater quantity of built area can make the city omed merube. Rav Moshe's answer focuses on the actual road: a way made for public passage remains physically open and used by the public. The greater quantity of wall elsewhere does not make that roadway into a physical wall.

Rabbi Levin applies the same issue to Brooklyn. Where a street capable of having the status of reshus harabim cuts through a claimed building-line wall, the status of the street must be resolved as part of the enclosure.

An exterior-wall analysis therefore needs both the standing-and-open measurements around the perimeter and the separate treatment of important public breaches. One aggregate percentage cannot supply the missing details about the individual street openings.

Bridges, tunnels and underpasses

Bridges and tunnels can change the physical geometry of a boundary in ways that a flat line on a map does not show.

A bridge may carry traffic directly through a riverbank, retaining wall or steep embankment used as the perimeter. The bank on either side can remain a valid wall while the bridge creates an opening through it. A broad bridge carrying public traffic requires analysis at the traveled opening itself. The lower wall cannot automatically be projected upward through the road surface by gud asik.

An underpass presents a different arrangement. The boundary might run above the roadway, beside it, or across the mouth of the passage. Each arrangement depends on the location of the actual wall and the correction used at the opening. Published construction material for the Crown Heights route includes a separate korah installed under an underpass to complete a tzuras hapesach. The construction itself illustrates that the underpass is treated as a physical passage requiring its own correction.

A tunnel requires the same kind of physical description. The relevant facts include where its entrance meets the claimed perimeter, whether a continuous wall remains at the traveled level, and what correction closes the opening. The published eighty-percent description does not supply that component-by-component information.

Highways and railways

Highways and rail corridors can provide long stretches of genuine physical wall. They can also contain major openings.

A highway retaining wall, solid barrier or qualifying fence can serve as a mechitza along its actual extent. A steep highway cut can qualify as a tel hamislaket where it has the required dimensions. Entrance ramps, exits, intersecting streets and underpasses divide those structures into separate physical sections that have to be measured and treated accordingly.

Rail corridors require the same precision. Solid retaining walls and qualifying fences can serve as walls. An embankment can qualify where its slope satisfies the required measure. Elevated tracks require the separate analysis discussed above. Bridges, street crossings, station access and gaps in fencing affect the continuity of the line.

Terms such as "the railway," "the highway" or "the embankment" therefore cannot substitute for a segment-by-segment description of the actual mechitza being counted.

Walls outside Crown Heights

A valid perimeter may encompass more than one neighborhood. A wall several neighborhoods away can therefore contribute to an enclosure that includes Crown Heights.

Its distance from Crown Heights leaves all the ordinary requirements of enclosure in place. The distant wall must connect into a complete valid perimeter, and the openings, public crossings and changes of structure between one segment and the next still have to be treated.

Exterior walls outside the neighborhood became especially relevant after they were publicized as a new basis for the Crown Heights eruv. The Crown Heights Beis Din addressed those walls directly in 5783.

The Crown Heights ruling of 20 Teves 5783

On 20 Teves 5783, Rabbi Avrohom Osdoba and Rabbi Yosef Yeshaya Braun issued a signed ruling on Crown Heights Beis Din letterhead. After reiterating the Beis Din's categorical rejection of the eruv, they addressed the newly publicized exterior walls expressly:

מובן ופשוט שאין כל שינוי בשלילה מוחלטת הנ״ל, גם לאחרי הפירסום ע״ד התקנת ״מחיצות״ כביכול מחוץ לשכונתנו

"It is understood and plain that there is no change whatsoever in the categorical rejection stated above, even after the publicity concerning the installation of purported 'walls' outside our neighborhood."

The ruling then repeats the practical psak:

שאסור בהחלט לטלטל ברחובות השכונה בשבת, ו״עירוב״ זה כמאן דליתא

"It is absolutely forbidden to carry in the neighborhood streets on Shabbos, and this 'eruv' is treated as nonexistent."

The letter states that the position had already been publicized by the local Rabbonim, naming Rabbi Aharon Yaakov Schwei and stating that it had earlier been the position of Rabbi Zalman Shimon Dworkin. The signatures on the 5783 document itself are those of Rabbi Osdoba and Rabbi Braun.

This 5783 psak was issued after the exterior walls outside Crown Heights had been publicized. The Beis Din referred to those walls expressly and stated that they produced no change in its categorical rejection. Its practical ruling remained the same: carrying in the neighborhood streets on Shabbos is prohibited.