How long was the rule of the dynasty that was active when the Rosetta Stone was inscribed?
Ptolemaic dynasty The Ptolemaic dynasty (Ancient Greek: Πτολεμαῖοι , "Ptolemaioi"), sometimes also known as the Lagids or Lagidae (Ancient Greek: Λαγίδαι , "Lagidai", after Lagus, Ptolemy I's father), was a Macedonian Greek royal family, which ruled the Ptolemaic Kingdom in Egypt during the Hellenistic period. Their rule lasted for 275 years, from 305 to 30 BC. They were the last dynasty of ancient Egypt.
Chronology of the ancient Near East The chronology of the ancient Near East provides a framework of dates for various events, rulers and dynasties. Individual inscriptions and texts customarily record events in terms of a succession of officials or rulers, taking forms like "in the year X of king Y". Thus by piecing together many records a relative chronology is arrived at, relating dates in cities over a wide area. For the first millennium BC, the relative chronology can be tied to actual calendar years by identifying significant astronomical events. An inscription from the tenth year of Assyrian king Ashur-Dan III refers to an eclipse of the sun, and astronomical calculations among the range of possible dates identify the eclipse as having occurred 15 June 763 BCE. The date can be corroborated with other mentions of astronomical events and a secure absolute chronology established, that ties the relative chronologies into our calendar.