סימן צה סעיף ב

עִיר שֶׁהִיא מֻקֶּפֶת חוֹמָה, אֲפִלּוּ הִיא גְּדוֹלָה מְאֹד, מְהַלֵּךְ אֶת כֻּלָּהּ וְעִבּורָהּ וּמִשָּׁם תְּחוּם שַׁבָּת. וְכֵן עִיר שֶׁאֵינָהּ מֻקֶּפֶת חוֹמָה וְהַבָּתִּים סְמוּכִים זֶה לָזֶה, כֹּל שֶׁאֵין בֵּין בַּיִת לְבַיִת יוֹתֵר מִן שִׁבְעִים אַמָּה וּשְׁנֵי שְׁלִישִׁים, נֶחְשָׁב חִבּוּר, וְשַׁיָּךְ לָעִיר, אֲפִלּוּ הוּא מַהֲלַךְ כַּמָּה יָמִים. וּמִבַּיִת הָאַחֲרוֹן, מוֹדְדִין אֶת הַקַּרְפֵּף וּתְחוּם שַׁבָּת.

A city surrounded by a wall, even if it is a very large [city], may be traversed over its entire area, including its outskirts, and it is from there⁹Rema 398: 5. Bi’ur Halachah rules like the Rambam, and others who say the karpeif is added only to connect two cities but it is not considered in calculating the techum of a city. that the Shabbos boundary is measured. A city not surrounded by a wall, but whose houses are close to one another, so that the empty space between one house and another is not more than seventy and 2/3 amos, is considered as joined together and belonging to the city, even if it would take many days to walk [from one end to the other]. And it is from the last house that the karpeif [enclosure] and the Shabbos boundary is measured.¹⁰Rema. Bi’ur Halachah is machmir and rules that we do not add a karpeif to a city that was extended by adding a house.

תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)