The Arioi were a secret religious order of the Society Islands, particularly the island of Tahiti, with a hierarchical structure, esoteric salvation doctrine and cultish and cultural functions. They included both men and women of all social strata, though men predominated. The Arioi principally venerated the war god 'Oro, whom they considered the founder of their order.
In order to understand the comparable societies on other islands of the Polynesian Triangle, it is necessary to understand Polynesian societal order in classical times, i.e. before Europeans discovered the islands. In most of Polynesia, society was strictly hierarchically structured and divided into several social strata. This division did not always manifest itself the same way, but it can be found in Tahiti, as well as in Samoa, Hawaii, the Marquesas Islands, the Austral Islands, the Cook Islands, all the way over on Easter Island, and even the remotest corner of the Polynesian Triangle.
There were in essence three castes on the Society Islands:
The system of power on the Society Islands included characteristics of both medieval European feudalism as well as the Hindu caste system.
The structure of the order of the Arioi was a mirror image of Tahiti's hierarchical society. There were several ranks; Moerenhout describes eight ranks which could be reached through initiation. Admission into the orders was relatively simple at first; thus, admission was associated with increasingly difficult requirements. Theoretically, all levels of all social groups were open to everyone, but in practice the highest classes of the Arioi were reserved for the highest classes of the nobility. The upper classes were occupied by priests, mostly the sons and daughters of the noble families in the upper classes, which guaranteed that the Arioi built up strong support for the absolutist ruling family.