By about 6000 BC, a Neolithic culture rooted in the Nile Valley. During the Neolithic era, several predynastic cultures developed independently in Upper and Lower Egypt. The Badarian culture and the successor Naqada series are generally regarded as precursors to dynastic Egypt. The earliest known Lower Egyptian site, Merimda, predates the Badarian by about seven hundred years. Contemporaneous Lower Egyptian communities coexisted with their southern counterparts for more than two thousand years, remaining culturally distinct, but maintaining frequent contact through trade. The earliest known evidence of Egyptian hieroglyphic inscriptions appeared during the predynastic period on Naqada III pottery vessels, dated to about 3200 BC.