An administrative unit or province of ancient Egypt, each consisting of a town or group of villages with its own guardian deity, district governor (nomarch), and symbol or standard. There were 42-44 such provinces in Egypt, varying over the course of the centuries, which ancient Egyptians called sepat. The system of division into provinces existed at least from the Old Kingdom (c 2575-2130 BC) and continued until the Muslim conquest (640 AD). In the Graeco-Roman period, whose temples are the source of the surviving lists of nomes, there were 22 nomes in Upper Egypt and 20 in Lower Egypt. In Ptolemaic times, a 'heptanomis' of seven nomes was formed in Middle Egypt. The Nile valley south of Ombos was sometimes regarded as one with the province of Nubia. The Nomarchs were appointed as delegates by the Pharaoh and tended to be autonomous chieftains in troubled periods.