Bava Batra 7 - Community-Enforceable Obligations
One whose home adjoins a common courtyard is obligated to contribute toward maintaining the privacy and security of the courtyard. If unwilling, he may be compelled to help build a gatehouse and a door for the courtyard.
A gatekeeper would sit in the shade of the gatehouse and prevent passerby on the public road from gazing into the courtyard. The door was used to keep outsiders from actually entering the courtyard.
How long must one be in the city to be treated like one of the citizens of the city? - 12 months. But if he bought a house, he is immediately treated like one of the citizens.