Limits, restrictions and, in some cases, prohibitions on the use of certain weapons have always fallen within the scope of international humanitarian law (IHL). The first formal international agreement to prohibit the use of a particular weapon was the St Petersburg Declaration of 1868, which prohibited the use of explosive projectiles under 400 grammes in weight. In the 150 years since then, many other treaties and agreements have restricted or prohibited the use of certain weapons in war. These particular examples of limiting or prohibiting the use of weapons are specific instances of the more general rule that belligerents do not have an unlimited power in the adopting of means of injuring the enemy.