Tamil social order was based on different ecoregions rather than on the Aryan varna paradigm, although the Brahmans had a high status at a very early stage. Segments of society were characterized by matriarchy and matrilineal succession—which survived well into the 19th century—cross-cousin marriage, and strong regional identity. Tribal chieftains emerged as "kings" just as people moved from pastoralism toward agriculture sustained by irrigation based on rivers by small-scale water tanks (as man-made ponds are called in India) and wells, as well as maritime trade with Rome and Southeast Asia.