MISHNA: Partners who wished to make a partition [meḥitza] in a jointly owned courtyard build the wall for the partition in the middle of the courtyard. What is this wall fashioned from? In a place where it is customary to build such a wall with non-chiseled stone [gevil], or chiseled stone [gazit], or small bricks [kefisin], or large bricks [leveinim], they must build the wall with that material. Everything is in accordance with the regional custom.

If they build the wall with non-chiseled stone, this partner provides three handbreadths of his portion of the courtyard and that partner provides three handbreadths, since the thickness of such a wall is six handbreadths. If they build the wall with chiseled stone, this partner provides two and a half handbreadths and that partner provides two and a half handbreadths, since such a wall is five handbreadths thick. If they build the wall with small bricks, this one provides two handbreadths and that one provides two handbreadths, since the thickness of such a wall is four handbreadths. If they build with large bricks, this one provides one and a half handbreadths and that one provides one and a half handbreadths, since the thickness of such a wall is three handbreadths. 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.

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.

GEMARA: The Sages initially assumed: What is the meaning of the term meḥitza mentioned in the mishna? It means a partition, as it is taught in a baraita: Consider the case where a partition of [meḥitzat] a vineyard which separates the vineyard from a field of grain was breached, resulting, if the situation is not rectified, in the grain and grapes becoming items from which deriving benefit is prohibited due to the prohibition of diverse kinds planted in a vineyard. The owner of the field of grain may say to the owner of the vineyard: Build a partition between the vineyard and the field of grain. If the owner of the vineyard did so, and the partition was breached again, the owner of the field of grain may say to him again: Build a partition.