Shortly after U.S. troops reached the center of Baghdad in April 2003, looters pillaged the National Archaeological Museum in the city. The National Museum was a storehouse of priceless artifacts from the earliest stages of Mesopotamian civilization; thousands of pieces disappeared in a day or two of looting and vandalism. International reactions were immediate and vehement; the U.S. government was roundly criticized for failing to secure the museum and prevent the looting. This Article explores international legal questions that arise in the aftermath of the events at the Iraqi National Museum. In particular, by failing to protect the National Museum and its treasures, did the United States fall short of any obligations under international law? The answer to that question hinges on the extent to which key provisions of the 1954 Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict have developed into rules of customary international law. This Article offers: (1) a general conception of the dynamic of international norm change, seen as an ongoing interaction among rules, actions, and arguments; and (2) an assessment of the emergence of international rules for the protection of cultural treasures in war. The analysis concludes that there is a plausible argument that the United States was under an international obligation to secure the Iraqi National Museum. Even if the American failure to protect the Iraqi National Museum did not violate a duty under international law, it will certainly play a catalytic role in the next stage of development of international norms.