Pax Codex (平和コード, Heiwa Kōdo?, lit. Peace Code) is a world's peace treaty from Final Fantasy Type-0. It was broken by Cid Aulstyne, leader of Milites Empire, by sending his l'Cie to attack other countries and collect their Crystals.
Two years after the cessation of hostilities, in 359, the heads-of-state drew up a peace treaty between the four Crystal-Nations. The treaty defined the four states' borders as they were at the beginning of the armistice. The Innsmouth Region would belong to Rubrum, and the Meroë Region between the dominion and the empire, was split.
The Crystals' power had waned as a result of the Crystal-States' use of them during the Great War and the will for peace was strong due to people's fear of the Crystal's disappearing. The Pax Codex outlined regulations for declaring war and capitulation, and humanitarian issues, such as treatment of POWs and civilians, and the use of l'Cie to encroach upon other nations was prohibited.
In 448 RG, the Fabula Pact was drawn up between the four peristylia forged by the heads of each peristylium as a non-aggression pledge. Being a non-governmental agreement, its contents—aside from the pledge for non-aggression—remain unclear.
In 842 Cid Aulstyne of the Militesi Empire breaks the treaty by deploying the White Tiger l'Cie to war to capture the other nations' Crystals. The other nations respond by deploying their own l'Cie, among other measures, and war once again sweeps across Orience.
Both pax and codex are Latin in origin, meaning "peace" and "book" or "tree-trunk" respectively.