In Mishna Eruvin 4:2, Raban Gamliel tells his colleagues "I looked out from our ship just before it got dark, and determined we were already within 2000 amot of the harbor."

Bartenura says he used some sort of tube to make this determination, and it sounds like it was specially marked for the 2000-amot distance. Sefaria's translation below ... I'm still clueless:

שכבר הייתי מסתכל. בשפופרת של קנה חלול שהיתה מתוקנת למדת צפיית אלפים אמה in the tube of a perforated reed that was properly prepared to the measurement of the clearness/viewing of two-thousand cubits.

Was this a telescope? Something else? How did it work?

  • Maybe the commentary of the Melekhet Shelomoh on this Mishnah might be an answer to your question: sefaria.org/…
    – Shmuel
    Jan 4, 2022 at 12:45
  • Rambam seems to imply a completely different tool?
    – Dov
    Jan 4, 2022 at 13:21

3 Answers 3


So this is a really fascinating topic that has bamboozled many meforshim and thinkers over the years.

The Talmudology website here helps to comprehensively break it down.

He first notes Rashi who says:

שפופרת - קנה חלול וכשהוא ארוך אין צופין בו למרחוק וכשהוא קצר צופין בו יותר והיתה שפופרת של רבן גמליאל מתוקנת למדת צפיית אלפים או בים או ביבשה

A tube: It was a hollow tube that when it is long you cannot see far though it and when it is short you can see farther. The tube of Rabban Gamliel was calibrated to measure 2,000 amot whether on land or sea.

When assessing this observation, the author asserts:

That sounds rather like a simple telescope in which the focal length may be changed. However, telescopes which use lenses to focus were invented (at least in Europe) only around 1608. We do not know the name of the inventor, though in October of that year a Dutchman by the name of Hans Lipperhey had submitted a patent for a telescope. Did Rabban Gamliel really use a telescope over 1,500 years prior to this patent?

He writes that modern day translations have analysed it as follows:

The Koren English Talmud suggests in a note that the tube was “a kind of precise protractor, similar to those used for astronomical measurements, i.e a type of sextant, the early form of which is known as an astrolabe.” The ArtScroll Schottenstein Talmud notes that Rabban Gamliel’s tube “operated without lenses, which were not invented until some fourteen centuries later.” It is challenging to figure out what exactly this tube was.

He notes how the mathematician and President of the Hebrew University of Jerusalem Selig Brodetsky (1888-1954) wrote a lengthy essay titled Astronomy in the Babylonian Talmud and notes that he finds it very difficult for Rashi to assert that it is a telescope given the period of the gemara and its relation to the technological advancement of the telescope.

As such, he moves on to the Rambam who views the instrument as being the astrolabe (like the Koren wanted to suggest).

שמסתכלין בו החוזים בכוכבים ונקרא בערבי אצטרל"ב ואיני רוצה להאריך ולהזכיר איך יושג כי זה הדבר בזה הענין ארוך ואפילו באריכות לא יבין זה אלא מי שידע בחכמת התשבורת

…It was the device used by astronomers and known in Arabic as an “astrolabe.” I do not want to go into lengthy details and describe how it is used, because it is a lengthy process. And even then only those who are especially knowledgeable will understand.

Another option is the possibility that it was the Nimrud Lens - discovered in 1850, it was a piece of crystal about 3,000 years old that appears to have been used to focus the rays of the sun, and perhaps even as a magnifying glass. There is however an academic dispute over its use, but at the very least it raises the possibility that people were using lenses long before the time of Galileo.

The author goes on to list various influential figures and their studies that hint to the possibility that the Rabbonim of the Gemara did in fact have access to some crude form of telescope or alternatively, "telescopes" served varying purposes throughout the ages.

Either way, his conclusions are as follows:

To sum, telescopes have served a number of different purposes for both rabbis and lay Jews.

  • For Rabban Gamliel it was used as a measuring device, (though it likely wasn't a telescope at all).

  • For Benjamin of Tudela is was a wondrous device to see for a distance of twenty days’ journey (though it was not a telescopes as we know them today, but some kind of mirror).

  • For Azariah Figo it was a device that taught a religious lesson: just as physical weaknesses may be overcome with human ingenuity, so too might spiritual weaknesses be overcome.

  • For Leon of Modena it was a proof of the greatness of Rabban Gamliel, who had used the device centuries before it was used in Europe.

  • For Avraham Yagel, it was was a similar message: the rabbis of the Talmud had previously invented the telescope, long before it began to be used in Europe.

  • For Joseph Delmedigo it was a scientific device that demonstrated the truth of the Copernican model.

  • For the Chofetz Chaim its invention reminded us of God’s providence in the world. Just as we can use the telescope to see high into the heavens, so too can God look down on us.

  • And for Vera Rubin, it was used as an object of honor for an extraordinary career.

  • 1
    What an astounding and intriguing answer! Jan 5, 2022 at 16:23

It could be a tube on a stand at a fixed angle. When looking through it you can only see what what its pointing at and you always know how far the furthest item is from you.

For an example how this device worked. Take a paper towel tube and attach it to a broom stick at a downwards angle, now look through it and see until where you can see now measure that distance, you now know every time you look through this tube what the distance is. Could be that Rabban Gamliel device worked like this and it seems to go with all the rishonim explanation.

A diagram on how it could work (sorry its the best that I could do on paint).

enter image description here

  • How does he account for elevation? Standing on a hill, or a house or a boat deck etc. That will scale up your triangle
    – Double AA
    Jan 5, 2022 at 3:29
  • Rabban Gamliel was at sea which makes it elevation 0ft above sea level. And regarding the boat deck could be it was designed with that in mind.
    – Efraym
    Jan 5, 2022 at 3:41

פַּעַם אַחַת לֹא נִכְנְסוּ לַנָּמָל עַד שֶׁחֲשֵׁכָה. אָמְרוּ לוֹ לְרַבָּן גַּמְלִיאֵל, מָה אָנוּ לֵירֵד. אָמַר לָהֶן, מֻתָּר אַתֶּם, שֶׁכְּבָר הָיִיתִי מִסְתַּכֵּל, וְהָיִינוּ בְתוֹךְ הַתְּחוּם עַד שֶׁלֹּא חֲשֵׁכָה: The mishna further relates that on one occasion, they did not enter the port [namel] until after nightfall on Shabbat eve. The others said to Rabban Gamliel: What is the halakha with regard to alighting from the boat at this time? In other words, were we already within the city’s limit before Shabbat commenced? He said to them: You are permitted to alight, as I was watching, and I observed that we were already within the city’s limit before nightfall. We acquired our resting place in the city during the twilight period. Therefore, it is permitted to walk throughout the city even after nightfall. - Eruvin 4:2

This is an interesting topic. It seems that Rabban Gamliel knew that they were permitted to alight, since he was watching. The Yerushalmi explains that he had a telescope (See: Yerushalmi Eruvin 5:3).

According to the Yerushalmi, Rabban Gamliel knew the hight of the towers in de area

Explain it if the port was larger than two bet se’ah, or the walls were not ten [hand-breadths] high but were not open wider than ten [cubits] nor what was standing was opposite what was standing and what was breached opposite the breached.

There is a interesting website called Talmudology where this is explained. They write:

So Rabban Gamliel could have used some high-school math to determine his distance from the shore, if he knew the height of the tower (AB) the angle (ACB), and the tan of that angle.

However, as they write further in the above mentioned article, it can be said that Rabban Gamliel did not know this kind of math, since:

However, no one had a notion of trigonometric function for more than 1800 years after that.

See however: Talmudology Redux - Readers Suggest How Rabban Gamliel Did It… where it shows an explanation taken from the ArtScroll Gemara.

ArtScroll writes (see the above mentioned link):

This distance is [previously] determined by placing the pillar on flat terrain, measuring out 2,000 amot, and placing an object at that distance.

  • 1
    Great minds think alike!...You missed the Talmudology article which expressly questions whether it is a telescope or not. See my answer :-)
    – Dov
    Jan 4, 2022 at 14:00
  • 1
    No not at all. This is very good as well!
    – Dov
    Jan 4, 2022 at 14:01

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