Norbourn was a river in the Northfarthing of the Shire. Between it and Brandywine River stretched Greenfields, where the Battle of Greenfields was fought. Norbourn is only mentioned in the detailed index Tolkien was preparing for the Lord of the Rings, but which was eventually left unfinished. In the partial map of the Shire published within the Lord of the Rings an unnamed river flows from the north to the Bywater Pool. It might be Norbourn, though it is also possible that Norbourn flowed straight to Brandywine more in the north.