Olympia: The Age of Gods PBEM (Oct 4 2000)
Certain skills, terrains, items and fortifications can affect the course of combat. In general, combat bonuses are computed by adding in any fixed bonuses, and then multiplying by any percentage bonuses. For example, a noble with an attack factor of 80, a magic sword with an attack bonus of +10, and Foresee Defense prayer of +10% would have an effective of attack of (80+10)*1.1 or 99.
A unit can benefit from one fortification bonus, one terrain bonus, one item bonus, and any number of skill or other bonuses. For example, a unit in a castle in the mountains receives both the castle defensive bonus and the mountains defensive bonus.