#thorakitai

The word thorakitai is generally translated to mean cuirassiers, referring to the armour they wore. A piece of art from the tomb of a soldier buried at Sidon (in modern Lebanon) is the main visual source for these guys and shows a man armed with a spear and thureos-style shield wearing a bronze helmet and a mail shirt, though it is possible that such soldiers might also have worn the linothorax armour that was commonly worn by other sorts of heavy infantry in the Hellenic world. Both the shield and mail were Celtic innovations and entered Greek service after Gallic Celts migrated east through Greece on their way to modern Turkey (where they became known as Galatians).

Though they are sometimes thought of as imitation legionaries, thorakitai were essentially an up-armoured version of the thureophoi, who were supposed to be a tougher form of peltast, who themselves were supposed to be light troops who were a bit more robust in a melee than pure skirmishers. You are essentially looking at the heaviest & most expensive form of a troop type who would normally be expected to hold the flanks of a hoplite or pike phalanx (depending on the era) and prevent them from being rolled up by the first good cavalry attack.