UPDATE: The Cities and Knights expansion can be downloaded for £2.99 / $4.99.

The third major expansion for the Settlers of Catan boardgame - Cities and Knights - is now available to Catan owners as an in-app purchase.

This particular adaptation of the core game is arguably the most violent, with aggressive barbarian hordes threatening to sail across the ocean and lay waste to your settlement at a moment's notice.

You will also encounter new cards and tech trees, which increase the likelihood of other settlers making off with your vital resources.

Raising the stakes

To give you a fighting chance, the soldier cards have been replaced with knights, which you can upgrade and use to defend your cities against attack.

Plus, if you improve your city sufficiently well, you can upgrade it to Metropolis status, which will give you both tactical superiority and sweet bragging rights.

iOS users can purchase Cities and Knights from the Catan in-game menu now. The Android version will be available "soon".