The mechanism of strain relief for compressively stressed Ag layers epitaxially grown on Pt(111) is studied by scanning tunneling microscopy. The strain in the compressed commensurate (1X1) Ag monolayer on Pt(111) is relieved in the bilayer by the formation of two weakly incommensurate structures: the metastable striped incommensurate phase, which converts into a trigonal network of domain walls upon annealing. This network is a general case for isotropic strain relief realized by the crossing of domain walls. The introduction of a phase shift of one set of domain walls allows the system to account for the energy difference of fee and hcp stacking. The stability of unidirectional via isotropic strain relief and the respective structures of domain walls is generally discussed for surface reconstructions and metal epitaxy of hexagonal-close-packed surfaces.