A couple more thoughts after looking at the save (I'm not trying to be harsh, but I think the situation is much more serious than I first thought):
1. You're more than halfway thru education and you still haven't switched to bureaucracy (I don't think you can afford the anarchy right now).

2. You have nothing to counter Rome's stack with. They will camp in the trees outside Odessa, and even if you collateral them you probably can't take that stack out.
3. I'd get as many units to Odessa as possible without leaving India naked. In particular, you have a GG heading towards Persepolis that could be used for a medic3 there (you have a M3 warrior in India, but you may need him there soon as well). You have some trebs near Odessa, so get as many there as you can. They will be nearly useless for attacking his stack outside of the city. But with the few seige Rome has, it will take 5 or more turns to bombard the defense down (unless he brings more trebs from somewhere). When it looks like the defenses will fall the next turn, move all of your units outside the city, let him take it, and then attack with the trebs. The cultural D will be gone, and your trebs will be able to do what they're made for: city attack. Also, most of your maces have CR promos, so this is where they will shine as well. Upgrade as many immortals/archers/spears as you can.
4. Will liberating Chengdu to Qin buy you a 10 turn peace treaty? It may be worth it.
5. Ashoka has guilds, and if Caesar trades him horses he will be able to make knights, which you really have no counter for at the moment.