How did Greek geography help Greece in the Persian wars?

As
the fifth century B.C. opened, the Persian Empire was moving westward in a quest to consolidate
control over the whole of the Near East. Then, in 499 B.C., reacting against the demand for
taxes and tribute, the Greek city of Miletus rose up against Persian rule. This revolt spread
from Miletus to the other parts of Ionia. Athens sent a naval force from across the Aegean Sea
and led a small force that took the Persian provincial capital of Sardis in the same
year.

In order to gain vengeance against Athens, the Persians, who lacked a
substantial navy, would themselves have to cross the Aegean Sea. In 491 B.C., the Persian
emperor Darius sent envoys to Athens, demanding its submission to Persian rule. The Athenians
not only rejected Darius's offer but also killed the envoys. The Persian army landed at Marathon
in 490 B.C., where the Athenians waited five days to engage the Persian forces for fear of being
outflanked by the Persian force. There are different theories as to why the...