At its session in Geneva in 1874, the Institute of International Law appointed a committee to study the Brussels Declaration and to submit to the Institute its opinion and supplementary proposals on the subject. The efforts of the Institute led to the adoption of the Manual of the Laws and Customs of War at Oxford in 1880. Both the Brussels Declaration and the Oxford Manual formed the basis of the two Hague Conventions on land warfare and the Regulations annexed to them, adopted in 1899 and 1907.
In case of bombardment all necessary steps must be taken to spare, if it can be done, buildings dedicated to religion, art, science and charitable purposes … on the condition that they are not being utilized at the time, directly or indirectly, for defense.
It is the duty of the besieged to indicate the presence of such buildings by visible signs notified to the assailant beforehand.