Sizable populations inhabit the valleys and highlands in scattered villages and small towns. Terraced mountain slopes, advanced irrigation systems, and sophisticated drainage canals in low-lying coastal areas provide ample fertile land for intensive agriculture. Politically people are organized in small and large independent chiefdoms; some control several dozen settlements, others one or more valleys. Despite frequent wars and conflicts, no group succeeds in establishing a state. Many peoples are ethnically related and in close contact through trade, but the variety in ceramic styles, metalwork, architecture, and burial practices reflects significant cultural differences. Construction of earth mounds (tolas) increases noticeably; stone is used for facing mounds and staircases, paving roads and plazas, and as foundations for buildings only in a few areas. Many groups continue to bury their important dead in shaft tombs with niches or side chambers or in urns; others inter them beneath mounds or house structures. Burial offerings include ceramic vessels and ornaments of semi-precious stone, shell, metal, and perishable materials such as textiles and featherwork. Metalworking using copper alloys continues. In many areas emphasis is on mass production of simple, small-scale ornaments rather than the manufacture of elaborate works bearing complex imagery as in earlier periods.