When Does the Film "300" (2007) Take Place?
"300" is a historical fiction war film written by Kurt Johnstad with Zack Snyder and Michael B. Gordon [adapting "300" (1998) by Frank Miller] that released March 7th, 2007. So when is "300" set?
It takes place in the year:
We know this because it depicts the famous and tragic Battle of Thermopylae which occurred sometime between July and October of 480 BC during the Second Persian War. As well as the build-up to it.

480 BC
We know this because it depicts the famous and tragic Battle of Thermopylae which occurred sometime between July and October of 480 BC during the Second Persian War. As well as the build-up to it.
Additionally, there is a prologue that ends as a storyteller says, "It's been more than 30 years since"... so it must take place sometime between 519 BC and 510 BC.
-480 - 30 = -510
or
-480 - 39 = -519.

