I do it the good old fashioned way- In RTW use a general of more than 5 Command- use him as a skirmisher to get this- 1 Urban Cohort and 9 either (on a budget) early leigionary cohorts or preferably 9 leigion cohorts. If I've got Rome I have a leigion first cohort, my best under 60 general and as many urbans as I can afford.

These legions tend to be used as armies that are always closely followed by a militia force and hopefully a manager in the stage of development who move into a city which the leigion has taken and enforce order. This leaves the mighty army of which I probably only have two in the empire free to take more cities.

An essential for a mighty infatry-based army is a fort each turn and a spy in the van to ensure they are almost impossible to ambush or attack with overwhelming force.