Bor which literally means a pit, is one of the Four Avos Nizikin - Primary Causes of Damage.

Varieties Although Bor literally means a pit, its laws apply to all stationary elements that cause damage to a moving entity. For example a person who poured water in a public domain, causing someone to slip, would be liable under the laws of Bor.[1] The pit can be in any form or shape.[1] Liability Generally the owner of the pit is liable for its damages. If a person digs a pit in the public domain, then he is considered its owner since he was the one created that damaging element.[1] Similarly if a person uncovers a properly closed existing pit, then the liability of damages falls upon him, rather then the pit's owner.[2] When a person purchases a pit or receives one as a gift, he becomes responsible for it.[4] Should a pit be formed on an individual's property, naturally or by an animal's, the responsibility to fill it falls upon him, and its damage liability.[4] If a someone was informed that pit was dug on his property by another person, it is his responsibility to cover it and damage liability falls upon him.[4] If someone sends a messenger to dig a pit, the messenger is liable and the sender is not.[8] Required Depth If a pit is less then 10 tifachim deep, he is liable for its damages but if a creature falls in and dies he does not have to pay since it was not deep enough to kill.[10] In a scenario where a pit is only nine tefachim deep, but the ninth tefach is filled with water, the pit's owner is liable even for fatalities. This is because a tefach of water possesses the same damaging potential as two tefachim of space.[11] If an animal felling a pit was only 8 tifachim deep with the lower two filled with water, or 7 tifachim deep with the lower three filled with water and died, the owner is not liable, yet if the plaintiff seizes assets on his own, he is able to keep them.[12] If a person dug a pit on his own personal property then in many cases he is not liable for its damages, however if the opening of the pit is located in the public domain or on another person's property, even if the main body of the pit is located in his own property, he is liable for its damages.[6] Digging Permissible Pits -If a person digs a pit with approval in a public area for the benefit of the community, his responsibility for it ceases once he transfers the cover to public representatives or informs the Beis Din about his intention to disengage himself from responsibility, requesting them to cover the pit.[7] - If a person dug a pit near the public domain in order to strengthen the foundations of a structure he is building, even if part of the opening extends into the public domain, he is not liable for the damages since the pit is temporary and he had the right to dig it.[9] When a person relinquishes ownership of his pit, thereby making it 'Hefker' or ownerless: -If the rights to the property are abandoned, but not those of the pit, the person is still liable for its damages, since he remains its owner. - If the individual relinquishes ownership of both the property and the pit, he is exempt from liability since, during its creation, the pit was dug permissibly on his personal property and now it is 'Hefker', he is no longer its owner. - If only the rights to the pit are relinquished the person is also free of liability because, like the previous case, the pit was originally dug permissibly on his property and now it is 'Hefker', he is no longer its owner.[6] If a person covered an open pit and then uncovered it again, liability depends on his method of covering: - If he used a regular cover, then when he uncovers it; liability reverts back to the original owner instead of himself. - If he filled it up with sand and then dug it up again, he is liable since the damaging element from the initial owner was completely removed.[3] Liability only applies to human created pits, if someone's animal digs a pit in the public domain or on another persons property, the owner of the animal is not liable for its damages.[5]

[1] Shulcan Aruch - Choshen Mishpat 410:1 [2] Shulcan Aruch - Choshen Mishpat 410:2 [3] Shulcan Aruch - Choshen Mishpat 410:3 [4] Shulcan Aruch - Choshen Mishpat 410:4 [5] Shulcan Aruch - Choshen Mishpat 410:5 [6] Shulcan Aruch - Choshen Mishpat 410:6 [7] Shulcan Aruch - Choshen Mishpat 410:7 [8] Shulcan Aruch - Choshen Mishpat 410:8 [9] Shulcan Aruch - Choshen Mishpat 410:9 [10] Shulcan Aruch - Choshen Mishpat 410:10 [11] Shulcan Aruch - Choshen Mishpat 410:11 [12] Shulcan Aruch - Choshen Mishpat 410:12