Ptolemy III Euergetes, (Greek: Πτολεμαῖος Εὐεργέτης, Ptolemaĩos Euergétēs, reigned 246 BC–222 BC) was the third ruler of the Ptolemaic dynasty in Egypt. He was the eldest son of Ptolemy II Philadelphus and his first wife, Arsinoe I, and came to power in 246 BC upon the death of his father. He is most noted for his invasions of the northern kingdom of Syria which he commenced upon the murder of his eldest sister Berenice Phernophorus; during this war, the Third Syrian War, he occupied Antioch and even reached Babylon. Ptolemy III was also the ruler who promoted the translation of Jewish scriptures into Greek as the Septuagint.
Ptolemy III Euergetes was responsible for the first known example of a series of decrees published as bilingual inscriptions on massive stone blocks in three writing systems. Ptolemy III's stone stela is the Canopus Stone of 238 BCE. Other well-known examples are the Memphis Stele (Memphis Stone), bearing the Decree of Memphis, about 218 BCE, passed by his son, Ptolemy IV, and the famous Rosetta Stone erected by Ptolemy V his grandson, in 196 BCE.
Ptolemy III's stone contains decrees about priestly orders, and is a memorial for his daughter Berenice. But two of its 26 lines of hieroglyphs decree the use of a leap day added to the Egyptian calendar of 365 days, and the associated changes in festivals.