@Eudaimon,
Greece, exhausted by inter-city and inter-league fighting was absorbed politically into the Roman Empire. Greek culture and philosophy was spread throughout the Empire, especially in Rome where the philosophers Cicero, Seneca, and Epictetus continued the tradition. Neoplatonism was born in Egypt, and spread throughout the Empire, as Runes notes:
"As a school of Greek and Latin philosophers, Plotinism lasted until the fifth century. Porphyry, Apuleius, Jamblichus, Julian the Apostate, Themistius, Simplicius, Macrobius and Proclus are the most important representatives. Through St. Augustine, Dionysius the Pseudo-Areopagite, John Scotus Eriugena, and the Greek Fathers, Plotinian thought has been partly incorporated into Christian intellectualism. Nearly all prominent Arabian philosophers before Averroes are influenced by Plotinus..."
Even with the disruption of the Empire by barbarian invasions and internal conflicts, Greek philosophy was continued in the Eastern Empire and by the Arabic commentators until its writings were brought to Europe and initiated the Renaissance.