Rail upon rail of costumes
What's the meaning of the phrase "rail upon rail of something"?
Is this a common phrase?
I guess it means many layers(a lot) of costumes, but I couldn't find it in the dictionary or internet.
In this context rail literally means a rail:
A bar or series of bars fixed on upright supports or attached to a wall or ceiling, serving as part of a barrier or used to hang things on
[emphasis added] http://www.oxforddictionaries.com/definition/english/rail
X upon X is a common construction in English, and means many Xs.
So rail upon rail means many rails.
I guess it means "lots of costumes", as in the amount of costumes is so massive that when you hang them up on racks/rails, they take up many.