Evidence of stone tool-making in the Turrialba valley suggests hunter-gatherers had settled in the area by 10,000 BC. The cultivation of corn, tubers and fruit trees developed over millennia, with small permanent settlements appearing from around 2000 BC in the northwestern province of Guanacaste. By 300 BC larger villages had been established in Guanacaste and across the Costa Rican Central Valley. Decorative objects made of jadeite, quartz and opal are testament to increasingly prosperous chiefdoms emerging between AD 300 and 800. The Diquis culture flourished across southern Costa Rica and western Panama between 700 and the early 16th century. It was famous for the manufacture of stone spheres up to two metres in diameter, whose significance remains uncertain.