From tankman's "What is UNLIMITED_MEN_ON_BATTLEFIELD do anyway?" question in the unlikely "Rome total war benchmarks!! HELP!!" thead, here:

Quote:

Reinforcement delays delays are caused by a setting in the preferences.txt file, namely UNLIMITED_MEN_ON_BATTLEFIELD:FALSE.

If you want to change it, then first back up Preferences.txt (make a copy somewhere), then open preferences.txt with notepad, change as below, then save and might as well backup to a new filename.

Set UNLIMITED_MEN_ON_BATTLEFIELD to be either TRUE or FALSE, like:

reinforcements delay
UNLIMITED_MEN_ON_BATTLEFIELD:FALSE

reinforcements do not delay
UNLIMITED_MEN_ON_BATTLEFIELD:TRUE

You can control a maximum of 20 units on the battlefiled (BF) at one time... that is an absolute limit, no matter what hardware you have! You can have more units on the battlefield, but they are controlled by the AI... not you (the human). These are called reinforcements. And the AI often does 'dumb' things with reinforcements. To use reinforcements (your units beyond 20) immediately this way, set UNLIMITED_MEN_ON_BATTLEFIELD:TRUE.

If UNLIMITED_MEN_ON_BATTLEFIELD:FALSE (the default), then your reinforcements (units past #20) will DELAY entering the battlefield, until you control less than 20 units. So if two units are killed, for example, you have 18. If you have another full stack waiting, then two more units will enter the battlefield from the standard battlesquare vector.

SECOND, SEPARATE ISSUE: AI CONTROL.

In the battlescroll which appears as the battle is initated in the strategic map, there is a computer icon which has a box beside it; if you uncheck this option, then you will control all reinforcements... up to 20, maximum. After 20, the AI gets the rest (if you set UNLIMITED_MEN_ON_BATTLEFIELD:TRUE).

Your own reinforcements will always arrive at the beginning of the battle, but you can still only control up to 20 units. If you let the AI control your reinforcement (the box is checked), then your reinforcements will cross the red line and join you immediately.

However, if you set UNLIMITED_MEN_ON_BATTLEFIELD:FALSE, then the AI will control all reinforcements.

EXAMPLE: Your scroll opens and you have 3 stacks. Your primary stack has 5 units, and the other two have 12 and 20. Your total units at combat initiation is therefore 5+12+20=37.

UMOB     AI Box       #Units on BF  When    #Units You  #Units waiting
                      (maximum)              control    to enter BF
======   ==========   ============  =======  =========== =============
TRUE   + Checked    =   37          Immed.        5**         0
TRUE   + UnChecked  =   37          Delay        20*         17*** 
FALSE  + Checked    =   20          Delay         5**        17
FALSE  + UnChecked  =   20          Delay        20*         17

Special notes:
* - You will control the reinforcement units when they actually enter the active BF.
** - The AI will control all your units on the active BF beyond your primary army stack, including those that are delayed.
*** - As long as you have 20 units on the field, your remaining units will await entry behind the red line; as some of your units die/leave the BF, these reinforcements will begin to enter, keeping you at 20.