The Delian League was led by Athens. The Delian League was formed in 477 BCE, in the wake of the second Persian invasion of Greece. It was an organization of city-states, under the direction of Athens, who came together to provide for mutual protection against future Persian invasions. The league, however, quickly devolved into an expression of Athens’ personal power which led to many conflicts within the league. It also led to the rise of the Peloponnesian League, led by Sparta, and the outbreak of the devastating Peloponnesian War.

The Battle of Thermopylae featured the last stand of King Leonidas during the Second Persian Invasion and is one of the most famous in history, making this answer the best choice. The Battle of Marathon brought the First Persian Invasion to a halt but was not a part of the Second, so it would not be a good choice. The Punic Wars were a series of wars fought between Rome and Carthage and did not involve Greece or Persia, so that would not be a good choice. The Battle of the Bulge and the Battle of Waterloo were both famous battles that happened thousands of years after the event in question, so they would not be good answers either.

In the aftermath of the Persian Wars, the city-state of Athens suddenly found itself in a position of unrivalled power in the Aegean and the rest of the Greek-speaking world. Athens, using its position as the head of the Delian League, was able to create something of an empire in a very short space of time. However, the Athenian Empire would last less than a century before it was torn down by the Spartans in the Peloponnesian War.

Xerxes I was the son of Darius I. All of the answers are Persian King of Kings, most of whom had direct animosity with the Greeks. But, only Xerxes I invaded (or ruled) in 480 BCE.

The Delian League was an organization of city-states and islands under the leadership of Athens. It was formed in the aftermath of the second Persian invasion of Greece and its stated goal was to provide mutual protection from possible future attacks.

Cyrus the Great was the founder of the Persian Empire. His conquest of the Ionian Greeks (those Greeks living in modern-day Turkey) in the sixth century BCE was the beginning of two centuries of conflict between the Persian Empire and the Greek city-states.

Herodotus wrote the first "history" text with his description of the Greco-Persian wars. Tacitus and Sallust are both Roman historians who cover the Roman Empire. Thucydides was a Greek historian who described the Peloponnesian War. Plato was a philosopher and student of Socrates.

Pausanias was a Spartan general who played an important role in the latter years of the Persian Wars. He led the Greek forces to victory in the decisive battle of Plataea in 479 BCE. He was then placed in charge of the Greek campaign to eradicate Persian influence from the Greek-speaking world. He would eventually come undone, however, due to the widespread belief that he was conspiring with the Persians to undermine Greek liberty.

Aristophanes is perhaps the most famous and celebrated of the ancient Greek comedy playwrights. Comedy was widely used in Greek society (particularly in Athens) to satirize and criticize society.

Sophocles is one of the three famous Athenian authors of tragedies, along with Aeschylus and Euripides. Sophocles’ most famous work is probably Oedipus Rex.