Research needed to build: None
Purpose: Defense bonus for defending troops.
Build in more then one town: Yes, will want them to increase defense bonus in each of your town/colonies
Soft Cap: lvl 24 Can build higher but after 24 the cost is greatly increased.
General Information regarding the Town Wall
Lets take a look around the window from the Town Wall's view(once you click on your on the Town Wall)
On the left side of the screen you will see
Here you can see how much materials will be needed to upgrade and how long it will take. Also you have the option to demolish the building as well. Clicking demolish will give you a confirmation screen showing how much resource you would recover. This option is helpful for when you want to abandon a colony and recover some of the luxury resources and wood.
Now in the middle portion of the screen you will see the following info near the bottom.
Defense bonus: Amount of defense bonus given to the towns defending ground troops, not naval units. Click here for a table on Wall Defense Bonus Calc
Possible breaches: One breach possible for attacker(s) for every one level of the town wall. Each breach gives the attacker a 10% attack bonus.
Attacks that failed at this wall: How many times the wall has been attacked.