Intercepting invaders
When someone is attacking you, you are give an option to intercept the army sent with in a certain amount of time. If you don't take that option in the time window then your city is attacked.
When the army is intercepted the battle would take place in a field or oasis. Depending on which one it is, the attacker or defender would receive a bonus of defense or attack power( or something like that).
This would allow a more strategic way to battle opponents and add another element to the game. Battles would continue in the same way when going up against a city. The only advantage of intercepting an invading army is you could get a bonus, which means that if you had a less powerful army it is possible for you to be the victor.
... Just a thought I had well raiding someones city.