The play Thyestes, written by Lucius Annaeus Seneca (known as "Seneca," or as "Seneca the Younger") in about 62 AD, is a classic Roman revenge tragedy.

The play is also an early example of a "closet drama," which is a play not intended to be performed by actors on a public stage, but to be read aloud, usually in small groups, and discussed for its moral and intellectual value, not its theatrical effect. The play has very little action, most of which occurs "offstage," and there is very little dialogue between characters. Instead, there are long monologues by individual characters, interspersed with commentary by the Chorus, and questions from minor characters.

Unlike most of Seneca's plays, and Roman plays in general, Thyestes is an original play, and although it's based on well-known mythology, it's not derived from an earlier Greek version.

The plot of the play involves two brothers, Thyestes and Atreus, and their rivalry for the throne of Mycenea. Atreus convinces Thyestes that he wants to share his rule of Mycenea with him, and when Thyestes appears to take what he considers is his rightful place next to his brother on the throne, Atreus tricks Thyestes into eating the cooked flesh of his own sons. (Shakespeare used this same basic plotline in his first tragedy, Titus Andronicus.)

Revenge

The theme of revenge looms large in Thyestes, based on a premise that was prevalent in Roman drama and revenge plays, that evildoers are individually responsible for their actions, that they must be punished, and that they are always deserving of the punishment they receive, no matter from whom they receive it, or how horrific it is.

ATREUS: Sceleri modus debetur ubi facias scelus, non ubi reponas. [Crime is limited when it is committed, not when the crime is repaid.] [Thyestes, Act 5] (Translations are contextual, not literal.)

In Atreus' mind, the punishment should not only equal the crime, but should exceed it.

Atreus doesn't seem to be concerned about the morality of revenge, only that there needs to be sufficient reason for the revenge, and that the revenge should be enacted without regret. When Atreus is questioned about his right to his revenge against Thyestes, he responds with the litany of Thyestes's wrongs against him in order to justify his revenge.

Tyranny and the misuse of power

This raises another theme in Thyestes, that of tyranny and the misuse of power.

Atreus uses his position as King to enact his revenge and commit unthinkable crimes against Thyestes. Atreus is questioned about this by Satelles, his attendant.

SATELLES: Fama te populi nihil aduersa terret? [Aren't you concerned about public condemnation of your acts?]

ATREUS: Maximum hoc regni bonum est, quod facta domini cogitur populus sui tam ferre quam laudare. [The greatest advantage of royal power is that the people are compelled to accept my deeds, and even to praise them.]

[. . .]

SATELLES: Vbi non est pudor nec cura iuris sanctitas pietas fides, instabile regnum est. [Where there is no morality, no concern for right, honor, virtue, or faith, the kingdom is unstable.]

ATREUS: Sanctitas pietas fides privata bona sunt; qua iuuat reges eant. [Honor, virtue, faith are for the common people; kings do what they please.] (Thyestes, act 5)

The play ends with Thyestes asking a pertinent question, then calling for revenge against Atreus.

THYESTES: Scelere quis pensat scelus? [Who punishes your crime?]

[. . .]

THYESTES: Vindices aderunt dei; his puniendum uota te tradunt mea. [The gods will avenge me; I pray to them for your punishment.] [Thyestes, act 5]