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Expedition to Persia and return to Rome

After having spent eleven years in Alexandria, he then decided, at the age of around thirty-eight, to investigate the philosophical teachings of the Persian and Indian philosophers. In the pursuit of this endeavor he left Alexandria and joined the army of the Roman emperor Gordian III as it marched on Persia (242–243). However, the campaign was a failure, and on Gordian's eventual death Plotinus found himself abandoned in a hostile land, and only with difficulty found his way back to safety in Antioch.

At the age of forty, during the reign of Emperor Philip the Arab, he came to Rome, where he stayed for most of the remainder of his life. There he attracted a number of students. His innermost circle included Porphyry, Amelius Gentilianus of Tuscany, the Senator Castricius Firmus, and Eustochius of Alexandria, a doctor who devoted himself to learning from Plotinus and attending to him until his death. Other students included: Zethos, an Arab by ancestry who died before Plotinus, leaving him a legacy and some land; Zoticus, a critic and poet; Paulinus, a doctor of Scythopolis; and Serapion from Alexandria. He had students amongst the Roman Senate beside Castricius, such as Marcellus Orontius, Sabinillus, and Rogantianus. Women were also numbered amongst his students, including Gemina, in whose house he lived during his residence in Rome, and her daughter, also Gemina; and Amphiclea, the wife of Ariston, the son of Iamblichus. Finally, Plotinus was a correspondent of the philosopher Cassius Longinus.