Weird naming conventions

[Mythos_Ruler]

Why were the Hastatii called thus, when it was the Triarii that used the Hasta?

[Jona Lendering]

I think nobody knows. The reconstruction of the early legions goes back to two antiquarian documents quoted by Livy: the Servian Reform (but quoted by Livy in a mid-republican redaction) and the description of the army during the Samnite Wars. It is simply not enough to reach certainty, although many reconstructions of the origin of the legion have been proposed. Personally, I think they're all piling hypotheses on hypotheses.