• Ptolemy (Ptolemaios) II Philadelphus (Πτολεμαίος ΙΙ Φιλάδελφος)
• Ptolemaic King of Egypt with Ptolemy I, Berenice I, Arsinoe I, and Arsinoe II
• Preceded by: Ptolemy I and Berenice I
• Succeeded by: Ptolemy III

Ptolemy II Philadelphus (309-246 BC), was of a delicate constitution, no Macedonian warrior-chief of the old style. E.J.Bickermann (Chronology of the Ancient World, 2nd ed. 1980) gives the date of his death as January 29.

His brother Ptolemy Ceraunus found compensation by becoming king in Macedonia in 281 BC, and perished in the Gallic invasion of 280-79 (see Brennus)

He began his reign as co-regent with his parents Ptolemy I and Berenice I from 288 BC-285 BC.

Ptolemy II maintained a splendid court in Alexandria. Not that Egypt held aloof from wars. Magas of Cyrene opened war on his half-brother (274 BC), and Antiochus I Soter, the son of Seleucus, desiring Palestine, attacked soon after. Two or three years of war left Egypt the dominant naval power of the eastern Mediterranean; the Ptolemaic sphere of power extended over the Cyclades to Samothrace, and the harbours and coast towns of Cilicia Trachea ("Rough Cilicia"), Pamphylia, Lycia and Caria were largely in Ptolemy's hands.

The victory won by Antigonus, king of Macedonia, over his fleet at Cos (between 258 and 256) did not long interrupt his command of the Aegean. In a second war with the Seleucid kingdom, under Antiochus II Theos (after 260), Ptolemy sustained losses on the seaboard of Asia Minor and agreed to a peace by which Antiochus married his daughter Berenice (ca. 250).

Ptolemy's first wife, Arsinoë I, daughter of Lysimachus, was the mother of his legitimate children. After her repudiation he married, probably for political reasons, his full-sister Arsinoë II, the widow of Lysimachus, by an Egyptian custom abhorrent to Greek morality.

The material and literary splendour of the Alexandrian court was at its height under Ptolemy II. Pomps and gay religions flourished. Ptolemy deified his parents and his sister-wife, after her death (270), as Philadelphus. This surname was used in later generations to distinguish Ptolemy II. himself, but properly it belongs to Arsinoë only, not to the king.

Callimachus, made keeper of the library, Theocritus, and a host of lesser poets, glorified the Ptolemaic family. Ptolemy himself was eager to increase the library and to patronize scientific research. He had the strange beasts of far off lands sent to Alexandria. But, an enthusiast for Hellenic culture, he seems to have shown but little interest in the native religion.

The tradition preserved in the pseudepigraphical Letter of Aristeas which connects the Septuagint translation of the Old Testament into Greek with his patronage is probably not historical. Ptolemy had many brilliant mistresses, and his court, magnificent and dissolute, intellectual and artificial, has been justly compared with the Versailles of Louis XIV.