Simplify the following text for a Grade 7 native English-speaking person.
Original: The Battle of Thermopylae ( , ; , MachÄ `` tÅ n ThermopylÅ n ) was fought between an alliance of Greek city-states , led by Sparta , and the Persian Empire of Xerxes I over the course of three days , during the second Persian invasion of Greece . It took place simultaneously with the naval battle at Artemisium , in August or September 480 BC , at the pass of Thermopylae ( ` The Hot Gates ' ) .
Simplified: The Battle of Thermopylae , 480 BC , was fought between an alliance of Greek city-states , led by Sparta , and the Persian Empire of Xerxes I. It took place at the pass of Thermopylae .