Longinus, Dionysius Cassius, a learned Greek philosopher, rhetorician, and critic, and eminent in all three departments, being in philosophy a Platonist of pure blood; his fame as a teacher reached the ears of Zenobia, the queen of Palmyra, and being invited to her court he became her political adviser as well as the educator of her children, but on the surrender of the place he was beheaded by order of the Emperor Aurelian as a traitor; he wrote several works, but the only one that survives to some extent is his “Treatise on the Sublime,” translated by Boileau (210‒273).
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Longfellow, Henry Wadsworth * Longmans