  Porphyry informs us that during the first ten years of his time in Rome, Plotinus lectured exclusively on the philosophy of Ammonius. During this time he also wrote nothing.  Porphyry tells us that when he himself arrived in Rome in 263, the first 21 of Plotinus’ treatises had already been written.  The remainder of the 54 treatises constituting his Enneads were written in the last seven or eight years of his life.