I'll try to be short and so not comprehensive.
I open a related topic: https://wildfiregames.com/forum/index.php?/topic/25503-special-buildings-and-so-on/
At some point there were beautiful units introduced. They were possibly introduced as experience, for art experiment, for special purpose or whatever.
Among them some stay in the atlas,
some other were moved to some maps in special already placed building (the famous Thracian black cloaks https://wildfiregames.com/forum/ind
Plutarch, Life of Aemilius Paullus, 18.5: "First the Thracians advanced, whose appearance, Nasica says, was most terrible, — men of lofty stature, clad in tunics which showed black beneath the white and gleaming armour of their thureos shields and greaves, and tossing high on their right shoulders rhomphaia heavy with iron."