The Collaborative International Dictionary of English v.0.48:

Gradin \Gra"din\, Gradine \Gra*dine"\,n. [F. gradin, dim. of
   grade. See Grade.] (Arch.)
   Any member like a step, as the raised back of an altar or the
   like; a set raised over another. "The gradines of the
   amphitheeater." --Layard.
   [1913 Webster]