[Peter Ebbesen]

Against the AI, at least, try massed Hydras. As soon as you have 5-10 in a group (placed in the middle front rank), it is nearly impossible for the AI to deal with them as they regenerate too quickly. [That should not prevent you from reinforcing with more Hydras as appropriate, just keep producing more of them]. Theurgs should be on the flanks a way back with bodyguards (and you will not be using ordinary troops for anything but bodyguarding here - it is so sad to waste your own men to your own poison). It is so easy it is almost cheating. [Remember to give Theurg communicants some item that can cast an offensive spell and set them to cast spells, or they will mindlessly charge into the fray and die from poisoning]

True, the Hydras do not move that far on the strategic map, but then, they do not need to... Against the AI. One Hydra army in each major theatre can pretty much block anything the AI throws against you.

You can then use an army or two of more mobile javelin troops to halt any incursion that manages to bypass the front lines anyhow.

(Against humans it probably works... Less well... As a human player can use individually targeted killer spells with precision 100 like paralyse, soul slay, incinerate &etc to take out your Hydras one by one)