Cheatham's question in an other thread got me thinking: there's actually many things a player can do to increase the campaign challenge without resorting to some fairly tricky or time-consuming modding. Here's what's within everybody's reach:
1. Allow unlimited men on the battlefield. To do this, open up the Preferences text file inside the Rome Total War folder, find the line about this there and change its value from "FALSE" to "TRUE", save and exit before you start the campaign. From now on, if you attack, say, a full stack enemy army which has another full stack army to support it close by, you will meet them both at the same time on the battlefield.
2. At the start of the campaign, do not allow unlimited time for deciding a battle. When night sets in your soldiers normally want to call it a day. So you'd better decide it within the time given, which could be troublesome, especially when assaulting a settlement with stone walls.
3. Set the campaign difficulty at the start of the campaign to "Very hard". Nobody likes you very much and tends to show it, too.
4. Set the battle difficulty at the start of the campaign to "Very hard". Enemy troops excel against you.
5. Apart from marching out against rebels, never start a war. In this way, the enemy is given the time it wants to build up its strength before initiating the fight. Every war you fight then also becomes just, a matter of self defence.
6. Accept every proposal for peace. When the enemy suggests a ceasefire, it has probably become too weak to pose much of a threat to you.
7. Never seek out an alliance yourself. The number of potential enemies is thereby kept at maximum as long as possible.
8. Never seek out a trade agreement yourself. This will limit your economic growth.
9. Never use assassins to kill off the enemy's generals before battle or seek to do this in an offensive way with other means during battle. With their generals, the armies of the enemy are worth more respect. And you are, if you beat them, worthy of more praise.
10. Never use spies to scout out unknown foreign territory. Blame an incompetent intelligence department for having to go out there and risk the disappearance of some troops.
11. Never use spies to scout out the composition of an enemy army inside or outside a settlement. The intelligence department is a joke. You'll have to take your chances with the potential presence of elite enemy units.
12. You wonder if the intelligence department is even capable of such a simple thing as opening up the gates of an enemy settlement from within.
13. When besieging a settlement, always resolve the matter by assaulting it on the battlefield as soon as possible. Never wait like a coward or couch potato for the settlement to surrender. Take on the full strength of the garrison and the towers on the walls firing away quite efficiently to support it. Automatic resolutions of assaults can be way too cheap a conquest.
14. When assaulting a settlement, avoid using the sapping technique to breach the walls. When you're left with other siege weapons to do the trick, as was more commonly the case in reality, stone walls are more of an obstacle to overcome (and thereby more worth their investment).
15. When assaulting a settlement, avoid using onagers to break the defence. You like it to be more of a sport and question of wits rather than brute force.
16. When assaulting a settlement without stone walls, avoid using long range missile units to decimate the garrison from a safe distance outside the walls before committing the close combat troops. In this game, wooden walls do not protect those inside as well as they should.
17. Never merge two or more units. The rivaly between them is too strong. Use them in their decimated condition until they can fight no more. Until then, as long as these battle-experienced units have a place in your army, your troops are not as strong numerically as they could have been. Might pose some problems when garrisoning a newly conquered settlement.
18. Let the AI manage most of or all your settlements. Just like your enemy, you don't have perfect control over the administration of the realm, so you'll have to make do with whatever resources this administration gives you.
19. Fight out every battle on the battlefield in the position the computer first found your army. Other positions within your theoretical deployment range in the landscape may be more advantageous and logical to hold, but your general was not smart enough to be there at the time of the clash.
20. Fight the battle as the general or his ranking officer, not as some detached RTW bird. When you fight as the general you adopt his point of view camera-wise and your vision of the battlefield is thereby restricted accordingly, making the tactical task decidedly more realistic and difficult. When you opt instead to fight as the general's ranking officer, the automatic genie has taken control of the general and you can only try to support his whims with the rest of the troops, which are all yours to lead as second in command. Watch out for the hot-tempered general taking his bodyguard on one of those foolish charges against the enemy again.
There you go, a simple way to a game with more nerve. There seems to be a whole bunch of people who want the game to be more challenging, so feel free to add simple tricks to this end in this thread, fellas.
PS: If the general is to be taken by an "automatic genie" his bodyguard must be grouped with at least one other unit and then put under AI assistance (with the button to the right of the "Group selected units" button).