Darius the Great's son, Xerxes wanted revenge on Athens for the great embarrassment they caused his father. So, he assembled an enormous invasion to end Athens. The Greeks, hesitant at which side to be on, were divided. Some Greek city-states sided with Persia, while others stayed loyal to their nation and sided with Athens. Xerxes, underestimated the Greek's fighting ability lost the battle at Thermopylae where they met on a mountain. The Persians though that they could easily push through the Greeks, but were surprised by their great ability. This held the Persians captive for three days, only to be advanced by a traitor who told the Persians of a secret path.