When faced with a larger attacking force...

[econ21]

Out of interest, How would you approach it if you were the attacker (with a smaller force) and the defenders were superior in number and again ranged in a long single line?

One useful tactic is the lure - try to induce part of the enemy line to break ranks and pursue you, e.g. by marching up a weak sacrificial unit that you then pull back. It is particularly effective if you have strong missile units and can hammer the pursuers. Even without missiles, you may be able to defeat the enemy piecemeal. It may be a little cheesy, but it work for William at Hastings...

More generally, I would try to provoke the enemy to attack - e.g. by raining missiles down on him - perhaps especially if I had manouvred to favourable ground (e.g. if I had gained a height advantage). I often find the AI does not make the best use of its missile units so if they are a big threat, I would try to take them out by preliminary "counter-battery" fire with my own missiles. Given him a screen of armoured or expendable targets in loose formation to fire on, while your missiles target his missiles.

Otherwise, I would try to flank the enemy, so that he is unable to use a double envelopment on my flanks and I can fight him on more even terms. If he is on a hill, try to manouvre so as to approach from the least steep angle and rest the ridge from him. I would aim to use "salami slicing" tactics again, of concentrating overwhelming force on a few of his units to break them and so demoralise (& ultimately chain rout) the rest.

Again, careful use of cavalry would be essential - I might leave the infantry to duke it out, outnumbered, but I would micromanage the cavalry so as to maximise their impact. Neutralising his cavalry or other elite units would be a particular priority. That's one reason for trying to induce the AI to attack - so he will advance his cavalry and you can deal with it before exposing your own.

But to be honest, I would try to avoid attacking a numerically superior enemy force. If you just stand your ground on the campaign map, the AI will tend to come to you and it is easier to defend than to attack. The only time I would attack would be when I either had a marked qualitative superiority (Romans or a high star general); or when the enemy had several separate stacks and I wanted to stop them uniting.