Peatlands are archives of extreme importance for the assessment of past ecological, environmental and climatic changes. The importance as natural archives is even greater in the case of ombrotrophic peat bogs, where the only inputs are atmospheric in origin. Here we integrated previously published physical and chemical results regarding the solid and liquid phase of peat with a biomolecular microbiological approach to assess the relationships between chemistry and microbial biodiversity along a Swiss bog profile corresponding to approximately 2,000 years of peat formation. The structure of bacterial and archaeal communities was assessed through a polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) approach followed by sequencing of PCR-DGGE bands of interest. Both chemical and microbiological data showed a differentiation of properties along the peat profile, with three major zones identified. Both bacterial and archaeal profiles clustered according to the depth (i.e., age) of samples. Among bacteria, Acidobacteria were recovered primarily in the first layers of the profile, whereas methanogenic archaea were more commonly recovered in the deepest part of the core, corresponding to the occurring anoxic conditions. Finally, a number of sequences had low homologies with known species, especially in bacteria: this points to an almost unknown microbial community adapted to the extreme conditions of peat bogs, which are acidic, rich in dissolved organic C, and predominantly anoxic.