Everyone probably already knows this, but, some may not, so:
When defending a city, it is good to have about 5 (2 at minimum) phalanx units in your city. Why? Take some of your units, and block off one of the streets the enemy goes down. Take some more and then block off another road the enemy goes down. Even if you have militia hoplites, this strategy works 95% of the time, against however many enemies. I have never seen it fail. Try placing your general behind for morale, and some missile units for added damage.
I should sell this.