"Use the Rally Point to launch attacks, send reinforcements and transport resources between cities and allies." - Global Warfare.
A Rally Point can only be built once in a city. Without a Rally Point, you will be unable to attack anyone. The number of marches and troops that can be marched is determineded by it's level.
Number of marches = Level * 1
Amount of troops = Level * 10,000
Note: Contributers, please input more information about the requirements and resources needed for each level. After the task has been completed, please erase this note. - Wolfden