There is a beautiful custom to recite “ma tovu, how goodly are your tents Jacob and your dwelling place Israel” (Bamidbar 24:6). These words uttered by the heathen prophet Bilaam as he attempted to curse the Jewish people are understood by our Sages as a reference to the modesty of our homes; specifically, that the entryways to the homes of the Jewish people were not directly opposite each other.
By having staggered entrances one would not be able to see into the home of their neighbour even if their doors were to remain open. It is this respect for the privacy of others that stands behind the 10th century cherem, decree of excommunication, issued by Rabbeinu Gershom for those who, without permission, read the mail of others.
And it is the basis of the opening Mishna of Bava Batra. “Neighbours who want to build a partition in the courtyard, they build the wall in the middle” (Bava Batra 2a). The Gemara explains that our Mishna is referring to a courtyard that is too small to divide. Nonetheless, if the neighbours agree, even a small courtyard can be divided. If the courtyard is large enough that each person has an area of four amot by four amot, roughly 6 feet by 6 feet, then a reluctant neighbour can be forced to contribute his share of the costs of the wall.
The requirement to build a wall is based on the premise that hezek reiya shmei hezek, damage caused by viewing is considered damage. This is quite unusual as generally, only direct and measurable damages can be acted upon. Thus, if one locks a person in his home so that they cannot get to work, while they have acted most egregiously, the courts cannot order him to pay monetary compensation, despite the fact that the other party suffered a real loss of money. Since this was an indirect loss, we apply the principle that grama bnizikin patur, indirect damages are unactionable.
Yet such is the importance of privacy laws that we force one to pay for a wall so that he will be unable to view his neighbours comings and goings. This holds true irrespective of the fact that no other courtyard in the city has walls, or that for years the members of the courtyard lived together without any need for a barrier. One’s previous silence is not regarded as acquiescence moving forward. This is quite striking. One of the major principles of Jewish civil law is hakol kminhag hamedinah, all is according to the custom of the place. This exact principle is used just a few lines later in the Mishna to determine the material to use, the thickness necessary and hence, the cost of the wall to be built.
It is a generally accepted principle of Jewish law that over time one can establish a chazaka, an ownership right to the use of property. If, for example, one does not protest others using one’s laneway, people will be granted an easement to continue using that laneway even over the protests of the owner and even if the property is sold to a new owner. It might have been argued that one who lives in an open environment for years forfeits the right to demand a wall be put up later. Yet invasion of privacy is akin to direct damages; furthermore while one may waive his privacy rights temporarily, one always reserves the right to demand they be honoured at a future date.
We live in an era where respect for the privacy of others has been greatly diminished. Contrary to the ethos of many, we generally do not have a right to know juicy tidbits about each other. At the same time too many people feel that the intimate details of one’s life should be – and today can be – broadcast around the world. The ancient Jewish teachings about privacy have much to offer the modern world.
 This does not mean that before Rabbeinu Gershom, reading someone else’s mail was allowed. It was forbidden. What Rabbienu Gershom added was that one who does so would be excommunicated, which in our tradition is a curse that the person drop dead. As such, there would be no mourning rites for one who dies while in cherem. Invasion of privacy is a very serious matter.