Techum shabbat
In Jewish halacha, the techum shabbat, or simply techum, is a limited physical area in which a Jew is permitted to walk on foot on Shabbat and Jewish holidays. In general, this area is calculated by measuring 2000 cubits in every direction from the place where a person was located when Shabbat began.
Discussion
Occupying a prominent position in the Sabbath legislation is the regulation of one's movement on the Sabbath day. These laws first date back to the Mosaic law, "...Let every man abide in his place; let no man go out of his place on the seventh day". Taking Israel's encampment in the wilderness as a prototypical model, some scholars view one's "place" as initially being within the radius of 12 biblical miles, corresponding to the encampment of the Israelites when they pitched their tents from Beth-jeshimoth as far as Abel-shittim. During Israel's encampment, it was permissible to walk the entire length and width of the camp on the Sabbath day. Later, by the conflation of multiple biblical passages which employ in them the words "place", "border", and "two-thousand cubits", the Sages found the basis on which to limit the movement of the people of a town on the Sabbath day to a mere 2,000 cubits, a boundary that would extend in any of the four cardinal directions, and which is measured from the last house built in the town's periphery. This limit of not proceeding beyond 2,000 cubits, or one biblical mile, is termed the "Sabbath limit." In ancient times, roads leading from the town were usually marked with rock cairns at the Sabbath limit, to aid travelers on the roads.Although the Scriptural verse clearly states, "...Let every man abide in his place; let no man go out of his place on the seventh day", the Aramaic Targum of the same verse renders its interpretation as follows: "...Let a man abide in his place, and do not carry any object from one domain to another domain beyond four cubits, neither let a man depart out of his place to venture beyond two-thousand cubits on the Sabbath day." Rabbi Yehudai Gaon and R. Achai Gaon explain the verse, "let every man abide in his place," as meaning that if he were uprooted from his place beyond the 2,000 cubits' Sabbath limit, either by a gentile or by an evil spirit, he is not permitted to move beyond four cubits of that place until the Sabbath has departed. Of these, R. Meir said that three cubits are for his body, and another cubit for him to stretch out his arms and his legs, while R. Yehuda says three cubits are for his body, and another cubit for him to retrieve an object from beneath his head and to place it beneath his feet, or vice versa.
The Sages of Israel permitted an Israelite to extend his "Sabbath limit" for another 2,000 cubits, in what is known as ʿeruḇ tǝḥūmīm, and which, if proper care had been taken on the eve of Sabbath to set-up a temporary abode at the prescribed 2,000 cubits' distance, would count as a man's Sabbath abode and would facilitate his going beyond the one biblical mile limit on the Sabbath day for another biblical mile. Setting up a temporary abode in this manner required of him to deposit on the eve of Sabbath enough food for two meals in an accessible place at the spot of the current 2,000 cubit limit, but did not require of him to actually rest there. He would also declare there, "Let my cessation of labor be in this place." For the ʿeruḇ tǝḥūmīm to be effective, the food must be prepared by day and be still in existence when Sabbath commences. Even so, this was a special allowance, and was only permitted when a certain religious duty or function warranted going beyond two-thousand cubits on the Sabbath day. Since the Sabbath day limit of 2,000 cubits was a rabbinic ordinance, the Rabbis had the power to exercise leniency in what concerns its proper observance. The Mishnah, however, prohibits a man from going out as far as the "Sabbath limit" and waiting there till nightfall in order to engage forthwith in some business activity or in labor otherwise forbidden to do on the Sabbath day, since by preemptively going out on the Sabbath day for such purposes, even if it is merely to wait there until nightfall to get an early start, he transgresses a different prohibition, that of not being absorbed in one's own personal business affairs and thoughts on the Sabbath day. If, however, it was merely to call back an animal that had gone astray, he is permitted to stand at the "Sabbath limit" and call out to his animal, and thereby have the animal come back within his domain on its own power.
Although a man has an extension of 2,000 cubits from his town or from the place that he makes his ʿeruḇ tǝḥūmīm, the Rabbis state that, from that central point of reference, the one traveling is to delineate the bounds outward as if it had been a square, rather than the arc of circle. The difference between these two systems of delineation is that if the Sabbath limit was merely measured outward in the form of the arc of a circle, the person has merely a radius of 2,000 cubits to walk in any direction. Yet, since the actual measurement is done in the form of a square, with the point of reference being in the center, this enables him to travel 2,000 cubits head-on, or about 2,800 cubits diagonally.
The starting point for measurement
A person who is located in an open area outside human settlement, measures 2000 cubits outside the "four cubits" surrounding him which are considered his personal space. If a person is located in an isolated house which is not part of a larger settlement, the techum is measured from outside the courtyard of his house. If he is within a settlement, the entire area of the settlement is considered his personal space.A person need not say or intend anything particular for this normal techum to take effect. However, he may declare that his "dwelling place" is located in a different place from his location at the entrance of Shabbat. For example: if a person is located just outside a city, he may declare that his dwelling place is within the city.
When this declaration is made in error, it is not valid. Therefore, a person who does not realize before Shabbat that he is adjacent to a city, and discovers this fact during Shabbat, may then enter the city and calculate his techum according to the city's techum. However, if he was aware of the city before Shabbat and knowingly chose his "dwelling place" to be based on his location outside the city, his techum remains as he intended, and if parts of the city are outside his 2000-cubit zone, he may not enter those parts.
Determining the city boundary
To calculate the techum for a city, it is first necessary to determine the city boundary from which the 2000 cubits are to be measured. A city may be of any shape, but the boundary used for this purpose is always a rectangle - the smallest rectangle which can contain the entire city. The measurement of 2000 cubits for a city's techum begins at the edge of this rectangle.Any house which is found within a distance of 70 cubits from the city is considered part of the city. If a second house is located less than 70 cubits from the first house, then it too is considered part of the city. By this principle, a "city" can extend over a large area even if its buildings are quite distant from one another. This is on condition that the buildings are used for dwelling, not for storage or other purposes. Of course, the rectangle enclosing the city will include even more space.
Two cities which have less than 141 cubits of open space between them are considered to be one city for the purposes of calculating techum.
When a group of nomadic people live in temporary buildings such as tents, their encampment is not considered a single settlement, and each individual measures 2000 cubits from his own dwelling. But if they built a fixed common structure such as a fence, they do count as a single settlement.