well osgiliath is a city that lies between minas tirith and minas morgul....the capital of gondor
by the time of the book it is in ruins from all the wars and is supposedly haunted
there is some mention about boromir + his brother faramir defending it in a big last stand kind of thing and i think they end up destroying a bridge to keep the forces of mordor away
or something... ill read up on it
brian