open city

noun
  1. a city that, during a war, is officially declared demilitarized and open to occupation, and that will consequently not be defended, in order to spare it, under international law, from bombardment or other military attack.
  2. a city or autonomous city-state that gives equal access and status to inhabitants and visitors without regard to religious, ethnic, racial, or national affiliation.

Origin of open city

First recorded in 1910–15
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018