The objective of Kingdom Alive is to defeat the enemy's tower as fast as you can. As well as trying to destroy your opponents tower you must also defend your own. There are 6 types of tower and each of which becomes unlocked when you collect all the heroes for the corresponding race.
The tower can be used to support your heroes on the battlefield so it is advised that you level it up as much as possible. The actual process of updating and leveling up the tower is similar to upgrading your heroes and commanders. The tower will become activated and be able to send a powerful blast when the crosshairs on the right hand of the screen come wthin reach of the monsters.
Below is a list of the towers from worst to best along with their stats (Level 1).
Siege Tower
ATK: 95
DEF: 37
HP: 3,300
Crystal Tower
ATK: 98
DEF: 53
HP: 4,000
Condor Tower
ATK: 101
DEF: 48
HP: 4,500
Magical Mobile Fortress
ATK: 93
DEF: 80
HP: 4,950
Tower of Dead
ATK: 89
DEF: 146
HP: 5,300
Spire of Light
ATK: 104
DEF: 114
HP: 5,800