Sefer HaChinukh 24

[Parashat] Vayehi Beshalach Pharaoh has one negative commandment in it. That we should not go outside of the boundary (techum) on Shabbat: That we have been prevented from going outside of the known boundaries on Shabbat, as it is stated (Exodus 16:29), “let no one leave his place on the seventh day.” And the explanation comes about this that “his place” is called anywhere that is no further than three parsa from outside of the city (Mishneh Torah, Laws of Sabbath 27:1-2). And a parsa is four mil, and a mil is two thousand ells. And we measure it from the outermost house in the city, even if it is as large as Nineveh. This is according to the law of the Torah, but the Sages made a fence and forbade that one should walk more than two thousand ells outside of the city.

From the roots of this commandment are that we should remember and know that the world is created and not primordial, as it is written explicitly about the commandment of Shabbat (Exodus 20:11), “For in six days the Lord made the heavens and the earth, the sea and all that is in them, and He rested on the seventh day.” Hence to remember this thing, it is fitting that we rest in one place; meaning to say that we not go to a faraway place, but rather only stroll and have delight [from our walks]. And the walking of [up to] twelve mil (the limit of what is allowed by the Torah) does not have much strain to it.

The laws of the commandment — for example, what is the law about one who spends Shabbat in the wilderness or in a cave (Eruvin 61b); and so [too,] one who goes outside of the boundary — volitionally or inadvertently, or by permission of the court (Eruvin 52b); what is the law if he surrounded himself with a partition on Shabbat (Eruvin 42a); what are the laws regarding the city of a house that goes out more than the other houses of the city seventy ells and a bit, a synagogue that has a domicile for the sextons, a house of idolatry that has domiciles for priests, or storehouses that have domiciles or three barriers that do not have a roof or pitch (Eruvin 55b); and how one measures a long or square or round city, or one that is made like the shape of a gamma or like an arch (Eruvin 55a); and with which string do we measure; and what is the size of the string (Eruvin 53b); and how does one measure from one valley to [another] valley, or to a mountain or to a wall; and upon whom do we rely for the measurement; and who is [considered] trustworthy to testify about the boundaries; and the rest of its details - are [all] found in the tractate that is built upon it, and that is Eruvin.

And [it] is practiced in every place and at all times by males and females. And one who transgresses and goes even one more ell than three parsa [outside of the city] is lashed. And so [too], if he goes even one more ell outside of the two thousand ells adjacent to the city, he is struck with rabbinic lashes for rebellion. And Ramban, may his memory be blessed, wrote (on Sefer HaMitzvot, Negative Commandments 321) that that which Rambam, may his memory be blessed, said in his Book of the Commandments (Sefer HaMitzvot) that the prohibition of boundaries is forbidden from the Torah past two thousand ells [from the city] — and so [too], what he said in his great composition (Mishneh Torah, Laws of Sabbath 27:1) that he recanted from this and wrote that the measurement of the Torah is three parsa — is all a mistake, since we do not have a prohibition of boundaries from the Torah at all. And so is it elucidated from many places in our Gemara, which is the Babylonian [Talmud] that we rely upon in all of our words. And the teacher (Ramban) gave numerous proofs for this on Commandment 313 (it should read, 321) of the negative commandments. And he understands, “let no one leave (yetseh),” to be like “let no one carry out (yotsi)” — [just] like there is an opinion in Tractate Eruvin 17b that understands it this way.