Related Rule
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
Section A. Establishment of open towns
France’s LOAC Manual (2001) defines as an open town “any inhabited area located in the combat zone or in its proximity, which is open to enemy occupation in order to avoid fighting and destruction”. It lists the following four conditions that must be fulfilled in order for a town to be considered an open town: all combatants as well as mobile weapons and military material must be evacuated; no hostile use shall be made of fixed military installations and establishments; the authorities and the population shall abstain from committing any act of hostility; no activities in support of military operations shall be undertaken. The manual gives Paris in 1940 and Rome in 1943 as examples of open towns during the Second World War. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 124.