Out of curiosity, why did you delete those two but kept the other unused four?

The other looked nice, so I wanted to make sure we could not use them instead of deleting them.

iber_monument.xml uses iberian_bull.png, not monument.png.
pers_ishtar_gate.xml uses pers_gate.png, not ishtar_gate.png.
lamassu.png and statue.png look nice, but as far as I'm aware, we don't have corresponding Assyrian respectively Greek sculptures.
That said, I'm not opposed to keeping unused stuff.

(However, gaia/fauna_elephant.png appears to be an unused copy of gaia/fauna_elephant_african_bush.png and could be deleted.)