The following rule adjustments allow play with 2 players. In addition to the standard game material, you'll need the two specific cards found in the box.
NOTE: it's suggested to play the game with 3-7 players, before trying out the 2-player variant.
The game proceeds the same way as it would with 3-7 players, the difference is in the management of the Free city. In addition of playing a card for their own city, players will play a card from their hand for the Free city as well.