Barns do nothing in Farmville. They are just buildings which you can build for decoration.
Build a moat
well you can this check this site http://farmville-3d-design.blogspot.com/ will show you how to build a 3d Design in farmville and more secrets
You don't you build it, you unlock it as a new farm when you are a higher level.
yes but you have to build it first
They mostly used rossetta stone and limestone :)
He built massive city walls and a moat
As protection from raiding elephants.
By using your plow tool or tractor.
The water-filled trench around a castle is called a moat.
You have to buy it. It is under buildings and it cost's 60 farmville dollars. farmville is giving them away free you DO NOT have to buy it however some people havent gottne theirs yet. You should have a pop up when u log on to farmville. then u ask friends to help you build it with boards and such.
I think that the 'trench' you are thinking of is a moat. You could say that it is a trench full of water that surrounds the castle. If you are not thinking of a moat then I am sorry.