Prusias fights a war against Byzantium in 220 BCE, then defeats the Galatians who his grandfather, Nicomedes I, had invited across the Bosporus.

The Delphic oracle establishes a festival in Magnesia to honor the goddess Artemis, who reportedly appears there in 220.

The architect Hermogenes of Priene erects the Temple of Artemis Leukophryena in Magnesia to commemorate her appearance; a sculptured frieze depicting an Amazonomachy decorates the building.

The geographer Strabo mentions this temple, the third greatest temple after those in Didyma and Ephesus, but considered finest of all for its proportions.

Demetrius of Pharos (the island of Hvar in present Croatia), now Illyria’s leading ruler, in 220 raises a fleet of ninety lembi, or lemboi (native ships of the Illyrians, lacking rams but possessing wider beams than typical warships of the day) and sails south of Lissus, in violation of the treaty of 228 with Rome, resuming piracy.

Demetrius makes several unsuccessful attacks on Pylos; then, taking fifty of the ships, …

…begins pillaging the Cyclades (Polybius, III.16.3-4).

Classical writers depict Ptolemy IV as a drunken, debauched reveler, completely under the influence of his disreputable associates, among whom Sosibius is the most prominent.

Cleomenes, imprisoned by Ptolemy, escapes in 219 and, after failing to raise a revolt in Alexandria, takes his own life.

Antiochus, following the defection of one of Ptolemy’s best commanders, is now free to conduct what will be called the Fourth Syrian War (219–216), and seriously threatens Egypt’s Syro-Palestinian territory, Coele Syria.

When the Seleucid ruler in 219 captures the important eastern Mediterranean sea ports of Seleucia-in-Pieria, Tyre, and …

…Ptolemais, …

…Ptolemy's disreputable associate Sosibius and the Ptolemaic court enter into delaying negotiations with the enemy, while the Ptolemaic army is reorganized and intensively drilled.

The threat that is sufficiently grave that, for the first time under the Ptolemaic regime, native Egyptians are enrolled into the infantry and cavalry and trained in phalanx tactics.

Philip soon wins renown by supporting the Hellenic League in its war against Sparta, Aetolia, and Elis (219-217).