Terrain and promotions. AN archer (base 3) fortifed, on a hill, defending a city, first strike, then include promotions can win when attacked by an unpromoted elephant. We'll need a few more specifics. Which if you don't understand what I'm asking, that's the problem.
On the first part of your questions, what do you mean by 5 people. If you're going to war and trying to capture a city, it's quite likely that you will need more than a single elephant and a catapult.