In those days the boundaries around a person’s field were marked by a row of stones. It was easy for the person next door to shift the stones in order to annex extra land to his own property. Hence the Torah had to warn him sternly, lo tassig g’vul re’acha – “Do not move your neighbour’s landmark”.
The problem must have arisen often in Biblical times; the warning is repeated by the prophet Hosea (5:1) and in the Book of Proverbs (22:28, 23:10). The Book of Job (24:2) identifies the main victims as the poor, the orphan and the widow; Isaiah (5:8) condemns the rich and greedy who “join house to house, field to field”.
Though the law was originally meant to apply only to Israel, the sages were adamant that appropriating other people’s territory was unlawful wherever it happened (Bava Metzia 107b; Bava Batra 89a; Rambam, Hilchot G’nevah 7:11, 8:1-3; Choshen Mishpat 376:1, 231:1).
Hassagat g’vul, removing a landmark, came to have a much wider connotation as a general protection of the rights of others. It was applied to the rights of the poor to glean in the field and even to a scholar’s rights to his intellectual property and a printer’s rights to the works he publishes.
Despite the advantages of business competition, in time it became unlawful to infringe upon another’s means of livelihood, especially if the person concerned had special expertise and had invested considerable funds and effort in building up his business.
The halachic sources devote much attention to the question of a professional encroaching on another’s practice and endeavouring to attract his clients. A rabbi too must respect the rights of another rabbi.
All in all, hassagat g’vul became a major ethical concept that said two things: mind your own business, and mind other people’s business from encroachment.