Siege warfare has been restructured from previous Civ games. Previous cities games relied entirely on garrisoned units for defense, whereas cities in Civ V now defend themselves and can attack invading units with a ranged attack expanding two tiles outward. Cities have hit points that, if taken down to zero, will signal the city's defeat to invading forces. Surviving an attack allows a city to recover a fraction (approximately 15%) of its hit points automatically each turn. In addition, any melee unit loses hit points upon attacking a city, dependent upon the unit and strength of the city which can be increased by garrisoning a unit or building defensive structures (e.g. walls).
