Most Difficult to Conquer

[Andy1984]

Note to myself: make sure you have sufficient artillery before you enter India.

Most difficult, less rewarding area? That must be the steppes for reasons mentioned above.

A good second would be Gaul. Pretty agressive, frightening soldiers (who are even pretty well armoured in the late game), paid by the full treasury of the Aedui. Worst of all: there are hardly any mines to be found there...