The initial stages of iron silicide growth on Si(111) were investigated using LEED, AES and STM experiments together with DFT calculations. In 1:1 stoichiometry, a cubic FeSi develops showing a (1×1) surface periodicity which is stable up to 300°C. The epitaxial strain energy stabilizes this bulk-unstable B2 (CsCl-type) phase for up to 250 Å thickness. The surface is Si terminated, the interface coordination of the so-called B8 type. After annealing at ≈ 600°C, a (2×2)-FeSi2 phase of higher Si content is observed which possesses cubic crystal structure. It is stable below 10 monolayers (ML) initial Fe coverage and grows in an island-like morphology. In the initial growth stage, however, a c(8×4) phase forms that completely covers the surface at 1.5 ML Fe content and appears as potential template for further growth of homogeneous films. The interpretation of atomically resolved STM images suggests that the film contains three Si and two Fe layers in B2 structure with vacancies on Fe positions. The vacancy arrangement seems to be responsible for the c(8×4) periodicity displayed by the Si adatoms in T4-position.