A set of custom battles, designed to challenge those of us who can't remember what it feels like to lose
In order to get hard battles followings works also:

Set the AI on defence mode

this prevents to acertaindegree:

a) the dumb ai charges
b) the broken phalanx lines

Choose the units wisely
(balance your unit setup elite/normals, heavy/light inf/cav for both you and the ai, a balanced setup also increases the chance of the ai being deployed in a costum eb formation)

You can make it more challanging by adding more elites to the ai faction, or give yourself less units...

I found this setup challanging

Player Makedonia

General
Thessalian Cav
Thracian Podromoi
3 deterophoroi Phalangites
2 Hysteroi Pezhetairoi
Agyrsapides
2 Thurophoroi (sp)
2 Kretan Toxotai
Agriani
Hypaspistai
Thracian Peltastai
Kuoroath (sp)
2 Hoplitai
Pheraspidae


AI Arche Seleukia

General
Podromoi
Hellenikoi Kataphraktoi
3 Kleruchi Phalangites
2 Pezhetairoi
Agyrsapides
2 Thurophoroi
2 Thorakitai
2 Peltastai
Hypaspistai
Pherespidae
Thorakitai Agyrsapides
2 Syrian Archers