The Thermopylae isthmus was located on the road to Athens, which ay only 190 kilometers to the south. On one side of the Thermopylae gorge was a steep and inaccessible rocky cliff, on the other side was the Aegean bay of Maliakos, which cut deep into the land. In the first narrowing, where the coastal road ran from Thessaly to Beotia and on to Athens, the isthmus was only 14 meters long. A stone wall was located there, which was further reinforced before the battle. Near the gate in the wall, the isthmus widened, but after passing about 1.5 kilometers, it narrowed to just two meters. It was at this point that the king of Sparta intended to give battle to the Persians. He knew that only in this way did his army have a chance to win over the much larger enemy army.
Xerxes decided to take this route because it was the shortest route leading to Athens, and it also offered the possibility of not being overly disconnected from the fleet at the same time. Although he could have bypassed Thermopylae and taken the route through the Kytinion Pass, but this route was longer and did not allow for the proximity of the fleet, moreover, it allowed the Greeks to organize ambushes.
