What did the Declaration of St. Petersburg of 1868 prohibit in warfare?

The Declaration of St. Petersburg of 1868 prohibited the use of explosive projectiles weighing less than 400 grams.1

This agreement was rooted in the principle that the only legitimate objective states should pursue during war is to weaken the military forces of the enemy. By limiting the use of such weapons, the declaration sought to prevent unnecessary suffering among combatants, establishing an early foundation for the international law of war regarding the methods and means of conflict.21