The Aghios-Phloros fen formed during the Holocene on the floodplain sediments of the Pamisos River. Initially (around 7 ka ago) clayey peat and other limnotelmatic sediments accumulated with a mean rate of 2.55 mm/yr. The plant litter was derived mainly from Cyperaceae and Sparganium, with minor contribution of Nymphaeaceae, Myriophyllum, Zygnemataceae and Pediastrum algae. Humification was not intense, and thus the peat displays high volatile matter content (expressed on dry, ash-free basis), as well as high H/C and O/C atomic ratios. High clastic influx at this time is reflected in the high ash contents. Upland areas around the fen were occupied by Pinus and Quercus spp., along with Ulmus/Zelkova, Carpinus orientalis/Ostrya, Corylus, Salix, Fagus, etc. and persisted throughout time. About 5.2 ka ago conditions in the fen became pure telmatic, clastic influx ceased, and the accumulation rate decreased (0.74 mm/yr). Peat was derived from the same plant material. Humification was intense, and peat displays a low volatile matter content, as well as low H/C and O/C atomic ratios. The evolution of the fen ceased 40 years ago due to drainage constructions and intense cultivation.