site of famous battle

[Centurio Nixalsverdrus]

- The battle has to be a Heroic Victory for one side OR a close victory, in which both sides lost at least 85% of their soldiers.

Nah, at least 50% loss for the winning side would be enough imho.

- Extraordinarily many men fought in this battle (at least 10'000 men alltogether)

That's almost unachievable and practically contradicts you first proposal of 200 against all odds...

- In a radius of 3 Coordinates around a site of a famous battle, the faction who once had won this famous battle will get a morale-bonus if fightig at or near the same spot where their ancestors had achieved a great victory.

I'd say the very tile is sufficient, plus you should get a huge morale malus if you were the loser! If you're Roman though, you should get a morale boost for having lost at this site.