Followers of this belief system commemorated two founders on the holiday of Eikas on the twentieth day of every month. In Naples, a circle of adherents to this belief system was led by Philodemus of Gadara, a client of Lucius Calpurnius Piso. Gravestones of many members of this movement include the inscription “Non fui, fui, non sum.” Every day, followers of this belief system recited the (*) tetrapharmakos, part of its “principal doctrines.” The founder of this belief system is praised for defeating the monster Religion in a poem that also discusses the clinamen, or “swerve.” For 10 points, name this (10[1])materialistic ancient philosophy expounded in Lucretius’ (10[1])De Rerum Natura, which taught that the highest good was ataraxia, the absence of pain. (10[1])■END■