Walls are extremely useful for protecting any base. Build a as many walls as possible. Instead of surrounding your entire base with walls,try to create sections,that way the enemies will have to break through multiple layers of walls in order to destroy your base. Note that air units ignore them and some ground units can shoot over them, but most units have to destroy walls to breach their way into the base.
|Property||Level 1||Level 2||Level 3||Level 4||Level 5||Level 6||Level 7||Level 8||Level 9||Level 10||Level 11|
|Amount of Titanium to Upgrade||400||2,400||11,000||25,000||70,000||180,000||450,000||1,200,000||2,250,000||7,000,000||9,000,000|