After the defeat of Acron,king of the Caeninenses, Romulus, the founder of Rome, "cut down a monstrous oak that grew in the camp, hewed it into the shape of a trophy [διεμόρφωσεν ὥσπερ τρόπαιον], and fitted and fastened to it the armour of Acron, each piece in its due order." (Plutarch, Romulus 16, 4; Bernadotte Perrin translation (1924))
Where the Greek denotes:
διεμόρφωσεν: 3rd person singular aorist active, "[he] gave [it] shape to"
ὥσπερ: adverb of manner, "even as"
τρόπαιον: noun singular neuter accusative "a trophy, tropaeum."
This event occurred somewhere around 750 BCE.
Now what is the affixing of enemy armor to do with "crucifixion?" Simple. The shape of a trophy in ancient Roman times was nothing other than a cross. Observe:
Here is a depiction of a tropaeum on Trajan's column.
Note well that it is shown in the shape of a cross and is dressed with enemy armor.
And here is Alexamenos' donkey-headed god, fastened to and suspended on a tropaeum.
This is the sort of thing that all Christian depictions of the Crucifiction are modeled on and what nearly all people including scholars think of when they hear the word "crucify" or its cognates.