Indigenous people in the Philippine Cordillera Region maintain legal pluralism by invoking several legal orders—customary laws, conflicting national laws, international law, and principles of human rights—to assert claims to ancestral lands. Although the U.S. Supreme Court in 1909 held that Philippine lands that had been occupied from time immemorial are presumed never to have been public, the Spanish colonial Regalian doctrine, derived from the explorer Magellan's claim of all lands in the Archipelago for the Spanish crown, remains the theoretical bedrock on which Philippine national land laws rest. Land not covered by official documentation, such as the highland areas occupied by indigenous groups who have not acquired legal titles, is considered part of the public domain. Recently, dam-building projects, logging concessions, and commercial farming in highland areas have spurred renewed efforts by indigenous groups to assert rights to ancestral lands threatened with flooding, deforestation, and dispossession.