Tip for fighting a superior enemy.

[bovi]

Raids would be a good idea, if you can divert any troops from the constant defensive. It won't stop the stacks from coming, but they'll be using a greater portion of poor troops.

[Veris]

You are correct in not splitting your troops up. The distance is manageable and I believe the computer will spend 2 turns minimum sieging any city with walls and maybe longer for stronger walls, so putting a minimal garrison in the cities and one strong army which is able to abuse the central position to its fullest should be enough to hold.

However, defending like that is never going to defeat the computer on VH unless they get simultaneously invaded on every other front and even then I'm not sure if they would let up much.

The Seleucids will not stop sending armies against you until something changes, so unless you want to wait for that to happen (a decade would be reasonable, but so would never) you either need to secede the territories you took from them, which generally stops the bloodlust, and then go conquer your weaker neighbors to the north and east.

The other option is to take to the offensive. A map of your campaign map would be useful, but just from the info you've given, it would seem likely that you could take the Seleucids south/east towns without too much trouble, at least initially. Leave your defensive, centrally positioned defensive army with as few units as you can (with all this fighting you should have several veteran units at least) and send a new army to go conquer the weakly defended Seleucid territories. In general the a.i has many cities without a sufficient garrison, so forced marches should be able to snag a few towns before they can sufficiently react. If they do have too strong of a garrison to attack immediately after your siege equipment finishes, then you should not waste time sieging but either move onto another, less defended city, or try to devastate the land enough and force them to come out of the city.

Usually a sudden offensive will get you good economical gains and change the focus of their attacks, thus potentially freeing your defending army to go and attack to the west as well. But I must make clear that you are only setting yourself up for defeat either militarily or due to boredom if you continue only to defend those cities they want so badly, because without a change to the money script they will not stop.

[NeoSpartan]

I agree with the advice given so far.

Field an army and send after the Seleucid towns. Keep some, others just raize to the ground and get some $$$. That way you can train more troops back home.

Once you get some momentum going it will be hard for the AI to stop you. Provided that you take only MINIMAL loses in each battle.

[Birka Viking]

Or u could play M/M and the game become much more balanced..The selucid dont send stack after stack after u. And I shall soon play h/m too see how many stacks they send then..
Cheers

[Cataphract_Of_The_City]

Create a cheap defencive force to defend you lands and gather the rest of your troops and capture a Seleucid province that will shorten your lines, i.e. making them have to pass by that city to attak the interior provinces. Now they will attack only this city. They will be able to concentrate but if you move your defensive troops there, it will be safe.

[Dubius Cato]

You can also try to place forts in any mountain pass, river ford, or other strategic place, or even build a limes with forts in any other map tile. Put some cheap (or understrength) unit in, and it will probably stop the AI for another turn. It gives you more time to scramble your forces, and maybe they call off the siege altogether and wander off. I always use this in the small accessible line in Lybia between the coast and the desert to stop the Ptolemaic stacks, you need a line of six or seven forts there, and another one with a defensive army that covers all of them.

[pezhetairoi]

Take Prophthasia, whose mines will give you enough to field at least one fullstack and a halfstack in addition. Once I took Prophthasia I was able to take the fullstack out on the offensive in the north against Antiocheia Margiane (another money earner) and Asaak, then switch half its troops to the southern army (guarding Ariana and Prophthasia, since once you take Margiana they don't bother Baktra anymore) and take the offensive against Karmana and Persepolis. Pura should not be bothered with unless there are significant forces there that could backstab you. The idea is to minimise your frontage, so try to expand until you have captured both Asaak and Persepolis. With those two, you will be able to raise your force to two fullstacks of second-tier troops, which will definitely be enough to beat the Grays every time, since they will rarely if ever hurl fullstacks at you before you threaten Susa.