The Greek heavy infantry defending the pass at Thermopylae were hoplites.
A hoplite was a heavily armed Greek infantryman who fought in a close-order formation called a phalanx. Hoplites carried a large round shield, a thrusting spear, and a short sword, along with body armour that could include a bronze helmet, breastplate, and greaves. Their overlapping shields and disciplined ranks were especially effective in a narrow space such as Thermopylae.
The defenders in 480 BC were drawn from several Greek city-states, not only Sparta. Spartan hoplites fought alongside troops from places including Thespiae, Thebes, Phocis, Locris, and other Peloponnesian communities. The terrain reduced the advantage of the much larger Persian army by preventing it from deploying all its forces at once.
Hoplites should not be confused with archers or peltasts. Peltasts were lighter infantry equipped with smaller shields and javelins, while cataphracts were heavily armoured cavalry associated mainly with later armies. Thermopylae’s defenders also included other types of personnel, but the characteristic Greek line infantry were hoplites.