Cities of Destiny contains many of the most important and innovative cities from all of history. Cities do not have effects like other Innovation cards. Instead, each has six icons, valuable for sharing and protection against demands (and for making your own demands!). When melded, Cities also have immediate effects that allow you to splay, draw cards, and even count as achievements.
With a City on your board, you can take the Endorse action, which allows you to double-use one of your Dogma effects each turn. Build your civilization on these mighty Cities, and emerge victorious over your foes!