Pretty much nothing has 2 HP any more because of the auto resolve problems. In my glance through the EDU, it looks like multiple hit points exist on:
- Generals' bodyguards
- Chariots
- Spartans
- German berserkers
EDIT:
I almost forgot. Legions start with very high morale values. This makes them hard to break. Aquila legions have the 'command' attribute, which adds to their morale. I'm not sure if multiple command units near one another reinforce the morale effect. If you add a good general (their command stars and their morale bonuses add to unit morale) and/or are playing on a harder difficulty (again, morale bonuses), the aquila legions may become virtually unbreakable. This would force you to kill them all without them routing. *shudder*