The Collaborative International Dictionary of English v.0.48:

Topple \Top"ple\, v. i. [imp. & p. p. Toppled; p. pr. & vb. n.
   Toppling.] [From Top summit.]
   To fall forward; to pitch or tumble down.
   [1913 Webster]

         Though castles topple on their warders' heads. --Shak.
   [1913 Webster]