The exact dating of Seneca’s plays is not possible to determine. There are no allusions to contemporary events in the Agamemnon. It possibly belongs to the first group of Seneca’s plays along with the Phaedra and the Oedipus, written in the later years (AD 50-54) of Claudius’ reign.
In the Agamemnon Seneca treats the well-known myth of king Agamemnon’s return from Troy and his murder by his wife, Clytemnestra, and her lover, Aegisthus, who is Agamemnon’s cousin. The place of the dramatic action is Argos (or Mycenae), the palace of Agamemnon. The time is the day of Agamemnon’s return from Troy after ten years of absence. The characters taking part in the play are: (1) The ghost of Thyestes, (…
Michalopoulos, Andreas. "Agamemnon". The Literary Encyclopedia. First published 06 October 2014
[https://www.litencyc.com/php/sworks.php?rec=true&UID=13468, accessed 20 January 2018.]