Cities can be purchased, if enabled, in Commerce games.
Cities are shown by a small house icon on the territory. If two or three cities exist on a territory, two or three houses will be shown. If four or more cities exist on a territory, the game shows the number of cities followed by the house icon.
Cities always provide one gold per turn to whoever controls the territory the city. If someone captures the territory, all income produced by the city goes to the new owner.
By default, cities cost 5 gold plus one additional gold for each city already on the territory. For this reason, it often makes sense to spread out your cities onto different territories, rather than stacking them all on your most defensible territory.
The base city cost can be customized by game creators.
To build a city, select the gold button below the commit button, select Build City, then select a territory you control to build a city there. If you change your mind before committing your turn, you can delete the build-city order out of the orders list.
Once a city is built, it can never be destroyed, unless done by a mod.
Blockading a territory with a city will not destroy the city. The city will simply be owned by neutral, who receives no benefit from the gold per turn. If a player later captures that neutral territory, they will then receive the gold per turn from the city.