The Watch Tower is the most important building in the game. As a defensive building, the higher the level - the more defense strength for your city.
The Watch Tower is the only building that can drop in levels. During an invasion, troops have the ability to reduce the level of the Watch Tower during an invasion. Once the building has dropped to Level 0, the city is vulnerable to invasion and can now be captured within an attack.
During an invasion, the Watch Tower can be reduced in level by incoming troops. This is determined by probability, based on the Sol Patrol "Type" rarity. Meaning the Type: Ranger will have a lower chance of reducing the level than a Type: Chief. After the Watch Tower level has dropped to Level 0, there will be a chance based on the "Type" rarity, that the city can now be conquered in the next attack. A player will also have a cooldown that will be randomly determined between 2 and 24 hours to increase the Level from 0 to 1. If Level 1 is restored, it will stop the next attack from potentially conquering your city.