The Ptolemaic Kingdom reached the height of its military and economic power during his kingship, as initiated by his father Ptolemy II Philadelphus.

On his succession, Ptolemy III married Berenice II, reigning queen of Cyrenaica, thereby bringing her territory into the Ptolemaic realm.

In the Third Syrian War (246–241 BC), Ptolemy III invaded the Seleucid empire and won a near total victory, but was forced to abandon the campaign as a result of an uprising in Egypt.

In the aftermath of this rebellion, Ptolemy forged a closer bond with the Egyptian priestly elite, which was codified in the Canopus decree of 238 BC and set a trend for Ptolemaic power in Egypt for the rest of the dynasty.

In the Aegean, Ptolemy III suffered a major setback when his fleet was defeated by the Antigonids at the Battle of Andros around 246 BC, but he continued to offer financial support to their opponents in mainland Greece for the rest of his reign.

[14] At Antioch, Ptolemy III went to the royal palace to plan his next moves with Berenice in person, only to discover that she and her young son had been murdered.

[15][13] Rather than accept defeat in the face of this setback, Ptolemy III continued his campaign through Syria and into Mesopotamia, where he conquered Babylon at the end of 246 or beginning of 245 BC.

[17] Early in 245 BC, he established a governor of the land 'on the other side' of the Euphrates, indicating an intention to permanently incorporate the region into the Ptolemaic kingdom.

[22] After his return to Egypt and suppression of the revolt, Ptolemy III made an effort to present himself as a victorious king in both Egyptian and Greek cultural contexts.

[23][24] At the new year in 243 BC, Ptolemy III incorporated himself and his wife Berenice II into the Ptolemaic state cult, to be worshipped as the Theoi Euergetai (Benefactor Gods), in honour of his restoration to Egypt of statues found in the Seleucid territories, which had been seized by the Persians.

At an uncertain date around 245 BC, he fought a sea-battle at Andros against King Antigonus II of Macedon, in which the Ptolemaic forces were defeated.

[28] Shortly after this, in 241 BC, Ptolemy made peace with the Seleucids, retaining all the conquered territory in Asia Minor and northern Syria.

[29] The conclusion of the Third Syrian War marked the end of military intervention in the Seleucid territories, but Ptolemy III continued to offer covert financial assistance to the opponents of Seleucus II.

He offered similar support to Attalus I, the dynast of Pergamum, who took advantage of this civil conflict to expand his territories in northwestern Asia Minor.

This probably involved direct conflict with Antigonus II during the Third Syrian War, but after the defeat at Andros in c. 245 BC, Ptolemy III seems to have returned to the policy of indirect opposition, financing enemies of the Antigonids in mainland Greece.

As a result, in 226 BC, Aratos of Sicyon the leader of the Achaian League forged an alliance with the Macedonian king Antigonus III.

[36] The Athenians instituted a state religious cult in which Ptolemy III and Berenice II were worshipped as gods, including a festival, the Ptolemaia.

[37] In November or December 222 BC, shortly after Cleomenes' arrival in Egypt and Magas' failure in Asia Minor, Ptolemy III died of natural causes.

He was responsible for the first known example of a series of decrees published as trilingual inscriptions on massive stone blocks in Ancient Greek, Egyptian hieroglyphs, and demotic.

The decree instituted a number of reforms and represents the establishment of a full partnership between Ptolemy III as pharaoh and the Egyptian priestly elite.

They emphasise his support of the priesthood, his military success in defending Egypt and in restoring religious artefacts supposedly held by the Seleucids, and his good governance, especially an incident when Ptolemy III imported, at his own expense, a vast amount of grain to compensate for a weak inundation.

Other construction work took place at a range of sites, including (from north to south): Ptolemy III continued his predecessor's sponsorship of scholarship and literature.

[44] Galen attests that he borrowed the official manuscripts of Aeschylus, Sophocles, and Euripides from Athens and forfeited the considerable deposit he paid for them in order to keep them for the Library rather than returning them.

[45] The most distinguished scholar at Ptolemy III's court was the polymath and geographer Eratosthenes, most noted for his remarkably accurate calculation of the circumference of the world.

In the 1930s, excavations by Mattingly at a fortress close to Port Dunford (the likely Nikon of antiquity) in present-day southern Somalia yielded a number of Ptolemaic coins.