The Collaborative International Dictionary of English v.0.48:

Amphitheatric \Am`phi*the*at"ric\, Amphitheatrical
\Am`phi*the*at"ric*al\, a. [L. amphitheatricus.]
   Of, pertaining to, exhibited in, or resembling, an
   amphitheater.
   [1913 Webster]

WordNet (r) 3.0 (2006):

amphitheatrical
    adj 1: of or related to an amphitheater [syn: amphitheatric,
           amphitheatrical]