Thermopylae—(480 B.C.)

Persians by Aeschylus (472 B.C.)

Histories by Herodotus (450 to 420 B.C.)

Antigone by Sophocles (441 B.C.)

Peloponnesian War by Thucydides (431 B.C.)

Oedipus Rex by Sophocles (429 B.C.)

Hippolytus by Euripides (428 B.C.)

Clouds, Lysistrata by Aristophanes (423 B.C., 411 B.C.)

Bacchae by Euripides (MIT version) (405 B.C.)

Education of Cyrus, Cyropaedia by Xenophon (430 B.C. to 354 B.C.)

Pro Cluentio, On Old Age, On Friendship by Cicero (106 B.C. to 43 B.C.)

On the Nature of Things by Lucretius (somewhere between 99 B.C. and 55 B.C.)

Letters by Seneca (possibly a better version on WikiSource) (65 A.D.)

History of Rome by (Titus Livius) Livy (64 B.C. to 17 A.D.)

Eunichus by Terence (died 159 B.C.)

Annals by Tacitus (56 to 117 A.D.)

Discourses by Epictetus (55 to 135 A.D.)