The dating of the tragedies is highly problematic in the absence of any ancient references. A parody of a lament from "Hercules Furens" appears in the "Apocolocyntosis", which implies a date before 54 AD for that play. A relative chronology has been suggested on metrical grounds but scholars remain divided. The plays are not all based on the Greek pattern; they have a five-act form and differ in many respects from extant Attic drama, and while the influence of Euripides on some of these works is considerable, so is the influence of Virgil and Ovid.