The Grassmannian manifold G(2,n) and flag manifold G(1, 2,n) are known to be homotopy equivalent to their respective combinatorial analogues MacP(2,n), MacP(1,2,n), which are simplicial complexes constructed from posets of oriented matroids and flags of oriented matroids. In this talk, I will prove that G(2,n) and G(1,2,n) are actually homeomorphic to these combinatorial analogues.