Block cellular automata (BCA) make local, parallel, synchronous and uniform updates of in nite lattices. In the one-dimensionalcase, there exist BCA with 11 states which are universal for computation. The Billiardballmodelof Margolusis a reversible two-dimensionalBCA which is able to simulateany two-register automatonand is thus universal. This simulationis achieved by embedding a logicalcircuitry with balls. The construction uses Fredkin gate and conservative and reversible logics.