  In this paper, we first reveal an intrinsic relation between non-abelian zeta
functions and Epstein zeta functions for algebraic number fields. Then, we
expose a fundamental relation between stability of lattices and distance to
cusps. Next, using these two relations, we explicitly express rank two zeta
functions in terms of the well-known Dedekind zeta functions. Finally, based on
such an expression, we show that all zeros of rank two non-abelian zeta
functions are entirely sitting on the critical line whose real part equals to
1/2.
  This is an integrated part of our Geo-Arithmetic Program.
