Why do you think Clytemnestra has Agamemnon tread on the purple tapestry?

Assuming you didn't know beforehand, how might you tell from the text of this play that Aeschylus is an older poet than Sophocles and Euripides?

Identify an exemplary theme, character, mode of performance, or piece of stagecraft in the Agamemnon, and use it to explain how tragedy works as a genre.