Mishnayos Bava Basra Perek 1 Mishnah 2

And similarly with regard to a garden, in a place where it is customary to build a partition in the middle of a garden jointly owned by two people, and one of them wishes to build such a partition, the court obligates his neighbor to join in building the partition. But with regard to an expanse of fields [babbika], in a place where it is customary not to build a partition between two people’s fields, and one person wishes to build a partition between his field and that of his neighbor, the court does not obligate his neighbor to build such a partition. Rather, if one person wishes to erect a partition, he must withdraw into his own field and build the partition there. And he makes a border mark on the outer side of the barrier facing his neighbor’s property, indicating that he built the entire structure of his own materials and on his own land. Therefore, if the wall later falls, the assumption is that the space where the wall stood and the stones belong only to him, as is indicated by the mark on the wall. Nevertheless, in a place where it is not customary to build a partition between two people’s fields, if they made such a partition with the agreement of the two of them, they build it in the middle, i.e., on the property line, and make a border mark on the one side and on the other side. Therefore, if the wall later falls, the assumption is that the space where the wall stood and the stones belong to both of them, to be divided equally.

וְכֵן בְּגִנָּה, מְקוֹם שֶׁנָּהֲגוּ לִגְדֹּר מְחַיְּבִין אוֹתוֹ. אֲבָל בְּבִקְעָה, מְקוֹם שֶׁנָּהֲגוּ שֶׁלֹּא לִגְדֹּר אֵין מְחַיְּבִין אוֹתוֹ, אֶלָּא אִם רוֹצֶה כּוֹנֵס לְתוֹךְ שֶׁלּוֹ וּבוֹנֶה, וְעוֹשֶׂה חֲזִית מִבַּחוּץ. לְפִיכָךְ אִם נָפַל הַכֹּתֶל, הַמָּקוֹם וְהָאֲבָנִים שֶׁלּוֹ. אִם עָשׂוּ מִדַּעַת שְׁנֵיהֶן, בּוֹנִין אֶת הַכֹּתֶל בָּאֶמְצַע, וְעוֹשִׂין חָזִית מִכָּאן וּמִכָּאן. לְפִיכָךְ אִם נָפַל הַכֹּתֶל, הַמָּקוֹם וְהָאֲבָנִים שֶׁל שְׁנֵיהֶם: