As the title says.

The translation of “The Persian Excursion” that I have mentions that whilst on parade, the hoplites had shields, red tunics, bronze helmets, greaves and spears but no mention of body armour.

During the battle of Cunaxa the hoplites charge and keep pace the Persian troops which would be difficult if they were wearing breastplates.

When Xenophon creates a light cavalry detachment during their retreat, the soldiers selected are issued “jerkins” and breastplates.

When Xenophon leads his hoplites up the hill, he struggles to keep up as he is wearing a breastplate (he was wearing one as he was riding a horse but dismounted and took a hoplite’s shield to show him up and lead by example).

Later in the mountains, a Spartan gets killed after a longbow arrow pierced through his shield and into the side of his “jerkin” but no mention of a breastplate.

Mentions of being ‘heavily armed’ nature of the Greeks tends to refer to their Hoplon shields rather than their armour.

The events of the story take part just after the Polynesian War where Greek hoplites began wearing less armour in order to make be more flexible. Greaves also started falling out of use even though it’s clear the 10,000 were wearing greaves.