When a player becomes inactive, his city will start to decline, and will be open to conquering. If the player was ranked earl or higher, his cities will go lawless four weeks after the last login. For a player ranked baron or lower, the time period is only two weeks. Cities also go lawless immediately once they are abandoned, or if the player chooses to restart.
You can send a baron to settle a lawless city, which costs the same resources as creating a new city (100k wood, 100k stone, 25k iron and 25k food), but you get the buildings already built. Non-castled lawless cities do not require an army to be sent with the baron, but castled lawless cities can only be taken by a baron and army sent from a castled city.
If a baron arrives at a lawless city that was settled after he left his home city, but before arriving at the lawless city, he will return to his home city with the 250k resources. If this happens, be prepared to have sufficient storage capacity available, or you will lose excess resources. If you abandon a city anytime after settling it, you will lose the resources and baron.
Lawless cities decay 1 level of building per hour, starting with the highest level buildings. Often, the town hall in a lawless city will have lost a few levels, which will require the new owner to upgrade the town hall to be able to build any new buildings.
Once a lawless city decays down to only 3 points, it turns into ruins. Ruins cannot be settled, and only last a few hours before disappearing completely. Lawless cities and ruins can be identified on the map by their gray color.