  Two-dimensional (2D) honeycomb lattices beyond graphene, such as germanene,
promise new physical properties such as quantum spin Hall effect. While there
have been many claims of growth of germanene, the lack of precise structural
characterization of the epitaxial layers synthesized hinders further research.
The striped layer formed by Ge deposition on Ag(111) has been recently ascribed
as a stretched germanene layer. Using surface X-ray diffraction and density
functional theory calculations, we demonstrate that it corresponds in fact to a
Ag$_2$Ge surface alloy with an atomic density 6.45% higher than the Ag(111)
atomic density. The overall structure is formed by stripes associated with a
face-centered cubic top-layer alignment, alternating with stripes associated
with an hexagonal-close-packed top-layer alignment, in great analogy with the
($22\times\sqrt3$) Au(111) reconstruction.
