The Triarii were the third row of soldiers in the Roman army. Less experienced troops with lesser equipment went first. If the first two rows didn't defeat the enemy, they would then fall back behind the Triarii.
As the best troops in the army, the Triarii were tasked with winning the battle when all else had failed.
From Wikipedia: In most battles triarii were not used because the lighter troops usually defeated the enemy before the triarii were committed to the battle. They were meant to be used as a decisive force in the battle, thus prompting an old Roman saying: 'It comes down to the triarii' (res ad triarios venit), which meant carrying on to the bitter end.
The goal is to communicate a balance of discipline, preparation, courage under fire, strength, effectiveness decisiveness, and the ability and willingness to act when others are scared or unsure.
Taking into account all of the above, please note that this will be a logo for an investment firm, not a defense company. As such, I would want to strike a balance between an image that references what the Triarii were and represented, without overemphasizing the military origin of the name.