Allegory is also represented in some surviving ancient monographs: the "Homeric Allegories" by an otherwise unknown 1st century BCE writer Heraclitus, the 2nd century CE Plutarch's "On the Life and Poetry of Homer", and the works of the 3rd century CE Neoplatonist philosopher Porphyry, particularly his "On the Cave of the Nymphs in the Odyssey" and "Homeric Questions". Many extracts from Porphyry are preserved in the scholia, especially the D scholia (although the current standard edition, that of Erbse, omits them).