Cities and Knights of Catan is the most recent major expansion to Settlers of Catan and it takes the game to a whole new level. You get to control your soldiers on the map instead of just having cards representing them, you get to research new special abilities, and barbarians now attack the island regularly. This game adds many layers of complexity to Settlers, making it much more interesting from a strategic perspective. I highly recommend this expansion to someone who has played Settlers for a while and is a big fan, or to someone who just loves strategy board games in the first place.
Cities and Knights of Catan box cover.
In Cities and Knights of Catan, you compete with 2 or 3 other players to be the first to 13 victory points. There are many changes in this game from the original such as the lack of a largest army card and any development cards. For your military needs you may now buy soldier tokens which are placed on the board. You can also upgrade soldiers to be more powerful. Soldiers are used to harass your opponents and, more importantly, to fight off the barbarian hordes which attack Catan every so often. These enemies live on a black ship which slowly moves closer to the island. Once they arrive at the island you resolve the attack. If the barbarians are defeated, the person with the most amount of knights gets an extra victory point. Otherwise, the player(s) with the least amount of knights turns a city into a settlement.
While knights are important in the game, let's not forget the other half of the title: cities. These are your major source of a new type of resource card which this expansion introduces, called commodities. There are three commodities: coin, paper, and cloth. Coin comes from ore, paper from wood, and cloth from sheep. You use commodities to increase your knowledge in three areas: science (paper), military (coin), and trade (cloth). Eventually, when you increase the research of an area enough, you will get a metropolis in that area. A metropolis is worth 2 victory points and is placed on top of any of your cities. That city can now never be destroyed by the barbarians. Much like the longest road, if someone researches more than you in an area then they take that metropolis from you. On your way to getting a metropolis you can also get useful special abilities from your research.
When playing Cities and Knights you now roll three dice on your turn instead of two. One of these dice is from the original game, another is the same as a die from the original game except it is red, and the third has different symbols on it. These two new dice are used to determine if the barbarians get closer to the island and to determine if anyone gets progress cards. Progress cards give a player many special advantages and have replaced development cards in the game. There are three different decks of progress cards, one for each area of research. Each deck has a different feel to the sort of bonuses they give. Blue progress cards usually deal with knights or the robber, yellow ones usually deal with trading, and green ones provide advatages for building new settlements or cities. These cards can be extremely useful and are far more powerful than the old development cards. You can also play as many of them as you like per turn.
There are more rules than this which I have left out, but you now have a good understanding of the basic mechanics this expansion adds to Settlers of Catan. It is definitely more cutthroat than the original game, especially when it comes to handling barbarian attacks.The progress cards also add a lot to the game and can cause some dramatic twists which are great fun. For example, there is one green progress card which you can play to switch any of the two numbers on the board (except 2, 12, 6, or 8). The addition of research via commodities is also a bonus to the game as it adds many new options to players when forming a strategy for victory.
Since Cities and Knights adds so much to the game, I recommend all players to participate in at least one game of the original Settles of Catan before playing this expansion. I personally like the experience of Cities and Knights a lot more than the original. I like it so much I rarely even play the original anymore, except when introducing others to Catan, and even then my goal is always to get them to play this game as soon as possible since it is so good. I have not met anyone who enjoys Settlers of Catan who does not also like Cities and Knights.
Cities and Knights of Catan costs $42, but amazon.com
often has sales in which it goes for around $33. There is also a 5-6 player expansion for Cities and Knights which provides pieces for more people to play. While this is obviously a blatant attempt to get more money from us poor Catan dwellers (why couldn't they put the pieces for this in the normal 5-6 player expansion?), it is still definitely worth having. It costs $20 and can be found here.