The effect of the Great Rings upon Men

[Inziladun]

Originally Posted by Mithadan

The Ringwraiths did not have bodies. Per Gandalf, their cloaks are real and gave "shape to their nothingness." When the flood of the Bruinen washed them away and several lost their cloaks, Gandalf mentions that they would have to make their way back to Mordor empty and shapeless.

Gandalf could simply have been referring to the visible forms, imparted by the clothing. I still don't see how ordinary horses would support an insubstantial being.