Eruvin 57 and 58 Nature trails on Yom-Tov and measuring the techum with Google Earth

Whereas most of daf 57 focusses on the extended boundaries of cities, in particular another possible leniency that according to some allows an additional 70+ amos to be added to the city- proper’s boundaries, the Mishna at the bottom of 57b takes us into new territory- the correct method for measuring the techum.

In a time where walking between close-by city’s was normal and often required, much effort was made by each community to measure and mark the techum of their city, and 2 people worked together to do this rather complex task.

This requirement, however, is FAR from obsolete and should be done in any community where leaving the halachik boundaries of the city on Shabbos or Yom-Tov is common- this would include walking between two suburbs of a city that are separated by more than 141 amos of open space, a fairly small area which is enough to make them considered two different cities halachically, as well as towns bordering natural areas where people like to enjoy the trails (Ramat Beis Shemesh being a great example, with our lovely nature walks.)

The method set out by Chazal, and hinted at in pessukim, was that a rope measuring 50 amos would be held at either end by each partner at chest level- after shifting forward 50maway from the city, this would be repeated until 40 such measurements had been taken, and the techum boundary would be marked at this point .

This process would be done 8 times, at each end of the 4 sides of the square/rectangle that the city had been fit into, after which the final process of squaring the techum itself could be carried out.

The Mishna tells us that ” אין מודדין אלא בחבל של נ’ אמה לא פחות ולא יותר” – We may only measure with a rope of 50 amos, no more and no less.

The Gemara bases this length on the passuk describing the width of the Mishkan’s courtyard. “ורוחב חמישים בחמישים” – its width was 50 with 50. The seemingly spurious “with 50” teaches us that it should be measured with a rope of 50 amos, and this seems to serve as a precedent that things which require precise measurements should be measured with a rope of 50 amos.

The Gemara understands ( as per Rashi’s explanation) that any more than this would be too hard to pull tight enough, resulting in some sagging and a shorter measurement for the techum.

Similarly, any less would result in too much stretching and hence a larger techum than required.

The Gemara proceeds to discuss what material the rope must be made of and seems to conclude that it needs to be made from flax, due to its relative accuracy.

Whereas the length of the rope used appears to be non-negotiable, it is still not clear whether the Mishna is telling us that a rope MUST be used, or simply that if a rope is chosen, it must fit the required length.

It is also not clear whether the Gemara requires the rope to be made of flax and nothing else or whether it is simply allowing anything as accurate as flax, and by “kal vachomer”, anything more accurate .

One Nafka Minah ( practical ramification) of the first question could be if one wanted to measure the techum with the car’s odometer, or with google Earth tools.

If the Gemara requires rope and only rope, then despite its greater accuracy and efficiency, this would not be acceptable.

If on the other hand a flax rope was simply the lower limit of how accurate the measure may be, then these modern tools would clearly be fine and perhaps even better.

In a Beraisa brought by the Gemara, Rabbi Yehoshua ben Chananya points out that there is nothing better for measuring than “chains of steel”, but the Navi ( Zechariah 2/5 , in a vision describing the future messianic period) describes how Yerushalayim will be measured with a “חבל מדה”( a measuring rope.)

Although at first glance this might seem to prove that the rope is an absolute requirement even when more efficient methods are available, it is also possible to interpret this in a way that is consistent with the second more lenient possibility.

It could be that Rabbi Yehoshua is not bringing the passuk to exclude more efficient or easier methods of measuring, but just to exclude steel chains or other bulky materials which though more technically accurate, are not usually used as measuring tools due to their heaviness .

After all, handling a 50- amah wide metal chain is hardly a simple task even for two strong men!

The phrase “חבל מדה” would then not be taken completely literal but would teach us that the method used for measuring must not only be reasonably accurate but also something efficient enough to qualify as a “measuring rope.”

It is also possible that Rabbi Yehoshua ben Chananya is not bringing the passuk as a stringency which comes to exclude more accurate or more efficient methods, but as a leniency to teach us that even though a rope is not the most accurate of methods, it is still acceptable!

In looking through the Rishonim, I did not see much discussion about this question, but was delighted to see that the Meiri actually interprets Rabbi Yehoshua precisely like the second suggestion above, and rules that steel chains ( and by implication other more efficient and accurate means ) certainly may be used .

He notes that some disagree and are stringent, and I found in my search that the Or Zarua (2/163-Eruvin) indeed does so.

Amongst the later Poskim, I have not found anywhere that the Shulchan Aruch or Rema discuss this issue, but did find that the Aruch haShulchan( O.C.399) takes it for granted that Rabbi Yehoshua came to exclude steel chains and that a rope specifically must be used.

As I first heard from Rav Asher Weiss שליט”א , the Rema ( C.M. 25/2) rules that even though we usually follow the rulings of the later authorities assuming that they have already seen and taken into account the rulings of the earlier authorities, if they were clearly not aware of an earlier authority’s ruling, a contemporary poseik can follow that earlier authority.

It is well known that the Meiri’s work was not known to the Mechaber, and while it might have been known to the Aruch haShulchan ( it certainly was to the Mishna Berura who quotes him) it is not clear how much of it was known to him.

Given that הלכה כדברי המקיל בערוב , there thus certainly seems to be strong reasoning in favor of following the lenient approach and using the modern tools of technology to measure the techum, provided it is done with the agreement of a top-level Talmid Chacham.

It should of course also be borne in mind that a car’s measuring device, as well as the standard distance tool on Google-Earth measures total distance including the vertical component of slopes.

In contrast, the laws of Techumim generally allow one to consider only the horizontal component of the total displacement between the two points.

As such, unless one uses technological tools that can measure the “as the crow flies’ horizontal component of the displacement, one could land up being much more stringent than required.

This brings up one more major leniency that could be applied to the “Table Mountain ” conundrum. (for those who have not seen the earlier posts, this is a unique feature of the City of Cape-Town, which surrounds the over 1000m base to summit peak on 3 sides. We have been discussing whether the entire mountain or parts of its can be included in the city-limits, given the rules of עבור העיר and the 4000 amos cut-off point.)

The vertical height of the mountain is well over 1000m above the sea-level neighborhoods- Up and down, that’s about 2000m from the “walking ” distance measured by google earth that can be deducted from the techum limits once one leaves the last house of the city (or from the 4000 amos cut off point for עיר העשויה כקשת!)-unfortunately, the almost 6000 metre gap measured through google earth between the two opposite legs of the city still seems to result in far too much empty space to include the whole mountain in עבור העיר.

These posts are intended to raise issues and stimulate further research and discussion on contemporary topics related to the daf. They are not intended as psak halacha.