There is such a thing as an arcade mode to R:TW, but I assume you are not reffering to that. It is turned off by default and gives unlimited ammo, no fatigue and near-unbreakable morale to all units. Most likely you have heard of the Rome: Total Realism modification for R:TW 1.2. It makes the game harder, more realistic (realitively speaking) and more fun. There are several other good mods out there too: have a look at for example SPQR and Darthmod. My personal favourite is Europa Barbarorum (exquisite historical detail and probably the most challenging mod around) but still in beta phase. You can view of them on the hosted mod forums of the Total War center. Keep in mind though, that these mods are made for R:TW 1.2 and come with the limitations of this version: unchallenging A.I. (even worse than in 1.5) and problems with the cavalry charge.