Chose a frontal assault as opposed to what? The pass at Thermopylae was closed by a phalanx of hoplite infantry.
They attacked it because there was no other way to go. You make it sound like they could have just flanked them. The Persians were not stupid.
It was a pass, not open ground. Your choices are: #1 frontal attack, or #2 embark your army and leave, with a huge delay in your invasion. Large armies did not move very quickly in those days. You couldnt just load the 250,000 of them into C-5s and fly off somewhere else.
Xerxes gambled that a frontal attack with overwhelming #s would eventually work (and it might have had the Greek infantry been of poorer quality, or had less resolve), but it failed. In retrospect it was a reasonable tactic to attempt to break through, you never know what success might be gained untill you make a foray.
As it was they eventually found a hidden trail the led around them (after a Greek traitor showed them), after 3 days of combat.
The Persians chose a poor spot to embark from, they should have planned for an initial invasion point where their #s would be telling, and they had room to manuever. History is always 20/20 in hindsight as they say...
Next lets talk about the Spitfire, and its relationship to Gettysburg!
