Addenda to the stage equipment available: there were triangular pivotable scene paintings that would allow three changes of scene painting. There were also thunder and lightning machines of some sort. Masks were introduced soon after Thespis first created an actor's role (Thespis reputedly started out with face-paint). The masks were made of linen and gypsum (something like wall-board crossed with papier mache?).
As for Euripides, what are the chief differences between this play and the Persians?
The intellectual milieu in which Euripides was writing this play was quite different from that of Aeschylus' Athens in 472. Socrates was, by this time, surely an acquaintance of Euripides. Also, the thought of Protagoras and Anaxagoras will have been known to him. Protagoras is the man who said "Man is the measure of all things: of the things that are, that they are, of the things that are not, that they are not."
The political milieu is likewise incredibly different: in 423, when the play was produced, the Peloponnesian war had started. Athens was at war not with a non-Greek enemy, but with fellow-Greeks. And the war was essentially a war between a strict militaristic Sparta who wanted Greek city-states to be "free" (but did not mind them being within her sphere of power) and Athens, an openly imperial power that ran its own affairs as a democracy, but ran its empire as an empire. Euripides was a pacifist.
Religiously, Euripides seems at the least sceptical. He openly criticizes Athenian religious practices in his plays, and questions beliefs in the gods of the state.
Specifically, the situation that seems to provide the background for the Suppliants was that in 424, the Athenian army was defeated at Delium in Boeotia by the Boeotians under command of Thebans. The Boeotians did not allow the Athenians to bury their dead until some time after the battle, which was serious business for ancient Greeks. It is not always absolutely clear what sort of an afterlife Greeks expected, but leaving dead unburied could deprive them of their afterlife.
So Euripides had a clear topical intent in choosing to depict Thebans refusing to allow burial of the dead after a battle. The background of the myth which Euripides is recounting is as follows. After Oedipus' downfall, his sons Polynices and Eteocles fought. Eteocles became ruler, while Polynices fled to Argos, where king Adrastus received him. Adrastus even gave Polynices one of his daughters in marriage. Polynices gathered a force under the commands of 6 other heroes, which made up the "Seven against Thebes" (Aeschylus has a play by that name). The Seven were all killed before Thebes (Polynices and Eteocles killed each other: they had been cursed by their father Oedipus) but the Thebans refused to allow their bodies or those of their troops to be collected for burial.
Theseus was, according to Euripides' version, the son of Aethras (mother) and Aegeus (father). Aethra was daughter of Pittheus, who was son of Pelops and Hippodameia. Pelops was the son of Tantalus and Dione. Tantalus was the son of Zeus and Pluto (daughter of Cronos). Aegeus, an Athenian king, was son of Pandion (Pandion was king at Athens, but was forced to leave: he became king of Megara: his sons returned to Athens). Pandion was son of Erichthonius (King in Athens) and Praxithea. Erechtheus may be another Athenian King in this line, but he seems indistinguishable at times from Erichthonius. Importantly, both Erichthonius and Erechteus are "earth-born." Cecrops is often claimed as the first King of Athens: he too is earth born.
The theme of being earth-born is essentially a claim to be the original inhabitants of a land, to be an ancient people. The Thebans too had myths of autochthony, but theirs involved Cadmus, who sowed the dragon's teeth. The teeth sprung up as warrior, 5 of whom survived and became the ancestors of the Thebans.
In sum, Theseus was an important Athenian hero who had an illustrious lineage going back to Zeus and the original kings of Athens. He is regarded as the Athenian national hero and, mythically at least, with being the inventor of democracy.
The play is clearly pro-Athenian, and is designed to praise the Athenians. The Athenians courageously go to war on behalf of justice for others.
It is equally clearly critical of war and pro-peace.
A suppliant is someone who engages in a ritual of supplication. The suppliant must clearly declare him- or her-self as a suppliant, and ask for help. Zeus protects suppliants. It is a sort of international law that one should not harm suppliants. The sacrosanctity of the suppliant is dependent on the convention that anyone or anything in a sacred area is not to be harmed. This is called asylia (compare English "asylum"). Frequently, the suppliant asks for acceptance into a community (compare the story which Phoenix tells in book 9 of the Iliad about how he fled to Peleus' kingdom and was received as a son would have been: think of the story in Herodotus (1.44) about how Croesus granted refuge to Adrastus, who then killed Croesus' son by accident). The sacredness of the suppliant was comparable to the Greek "international law" convention of guest-friendship. Harming a suppliant could result in divine retribution or human effort to secure justice.
Typically, the suppliant takes a seat at a hearth, cult statue, or altar, which indicates that he or she is a suppliant. The suppliant also lays an olive branch with wool wrapped around it on the altar, hearth, or statue base, or carries it. The suppliant supplicates a particular person by certain stereotypical gestures including grasping the person's knees, touching the person's chin and hands. This is what Thetis did to Zeus in the Iliad when she made supplication to Zeus on Achilles' behalf.
A note about the translation: our translator is trying to preserve level of speech as well as meaning. Hence he uses colloquialisms (everyday speech) where he thinks Euripides did. He is also trying to produce some semblance of the meter (see P. 76).
Important passages in the Suppliants:
Theseus' anthropology 199-253
Aethra convinces Theseus to fight 311-377
The debate between Theseus and the Theban herald 412-475
Adrastus recounts the virtues of the 7: 867-927
Iphis' lament 1095-1126
Athena's directions 1197-1240.
Structure of the Suppliants:
1. Aethra and Choruses (and Adrastus): 1-87.
The chorus supplicates Aethra for help.
2. Theseus, Adrastus and Aethra and choruses: 88-377
Theseus learns the situation, refuses to help, is prevailed upon by his mother, and agrees to help.
3. Choral Ode: 378-393
Athens, help Argos!
4. Theseus, Theban herald, Adrastus, choruses: 394-609
Theseus and herald debate political systems. Herald tries to dissuade Theseus from helping.
5. Choral Ode: 610-645
Chorus worries about expedition.
6. Messenger, Adrastus, Chorus: 646-790
Messenger recounts battle. Adrastus laments for losses, rejoices in Theseus' victory.
7. Choral Ode: 791-806
Glory and Grief.
8. Chorus and Adrastus: 807-847
Woe.
9. Theseus, Adrastus, Chorus: 848-965
Aristeia of the heroes, rites arranged.
10. Choral Ode of Mothers: 966-995
Wretchedness of the death of a son.
11. Evadne, Iphis, and Chorus: 996-1126
Death of Evadne.
12. Choral Ode: 1127-1178
Mourning and resolve on vengeance.
13. Theseus, Adrastus, (and chorus): 1179-1196
Theseus binds Argives to Athens.
14. Athena and rest: 1197-end
Athena's Directions.