from the 10th–16th centuries include Maynila, Tondo, Namayan, Pangasinan, Cebu, Butuan, Maguindanao, Lanao, Sulu, and Ma-i. Among the nobility were leaders called datus, responsible for ruling autonomous groups called barangay or dulohan. When these barangays banded together, either to form a larger settlement or a geographically looser alliance group, the more esteemed among them would be recognized as a "paramount datu", rajah, or sultan which headed the community state. There is little evidence of large-scale violence in the archipelago prior to the 2nd millennium AD, and throughout these periods population density is thought to have been low. Social classes The early polities were typically made up of three-tier social structure: a nobility class, a class of "freemen", and a class of dependent debtor-bondsmen: Datu (ruling class) Maginoo (noble class, where the datu ascends from) Maharlika (warrior class) Timawa (freemen) Alipin (dependent class), classified into aliping namamahay (serfs) and aliping saguiguilid (slaves) Other political systems by ethnic group In Luzon In the Cagayan Valley, the head of the Ilongot city-states was called a benganganat, while for the Gaddang it was called a mingal. The Ilocano people in northwestern Luzon were originally located in modern-day Ilocos Sur and were led by a babacnang. Their polity was called Samtoy which did not have a royal family but was headed as a chieftaincy. In Mindanao The Lumad people from inland Mindanao are known to have been headed by a datu. The Subanon people in the Zamboanga Peninsula were ruled by a timuay until they were overcame by the Sultanate of Sulu in the 13th century. The Sama-Bajau people in Sulu who were not Muslims nor affiliated with the Sultanate of Sulu were ruled by a nakurah before the arrival of Islam. Trade Trade with China is believed to have begun during the Tang dynasty, but grew more extensive during the Song dynasty. By the 2nd millennium CE, some Philippine polities were known to have sent trade delegations which participated in the Tributary system enforced by the Chinese imperial court, trading but without direct political or military control. The items much prized in the islands included jars, which were a symbol of wealth throughout South Asia, and later metal, salt and tobacco. In exchange were traded feathers, rhino horns, hornbill beaks, beeswax, bird's-nests, resin, and rattan. Indian influence Indian cultural traits, such as linguistic terms and religious practices, began to spread within the Philippines during