What really happened and why was this festival so important to the Spartan race?
The script in the movie was over dramatized based on my reading of Herodotus, who states that a small Spartan force was purposely sent north to reconnoiter the Persians and provide psychological support for the Greek allies, whose resolve was wavering. The Spartans, from the beginning, intended to send the rest of their army as soon as the festival was over. Unmentioned was the fact that the allies were also constrained from sending full armies because the Olympic Games were going on at the same time.