Objective: To characterize patterns in the taxonomic diversity of parasites infecting the population of Aalst, Belgium, between the 12th and 17th centuries.Materials: 14 sediment samples from seven cesspits dated 1100-1700 CE.Methods: Digital light microscopy and Enzyme-linked immunosorbent assay (ELISA).Results: We identified eggs of four species of helminths: whipworm (Trichuris trichiura), roundworm (Ascaris lumbricoides), Echinostoma fluke and Dicrocoelium fluke. ELISA results for protozoal parasites were negative. Conclusions: Taxonomic diversity of parasite infections remained constant from the 12th to the 17th centuries. Roundworm and whipworm, spread by poor sanitation, were dominant. Two species of zoonotic parasites were also identified, including for the first time ever in the Low Countries the Echinostoma fluke, which may have been spread by eating uncooked freshwater animal foods.Significance: Analysis of sediment samples spanning such a broad chronology (six centuries) from a single city offers the opportunity to track diachronic change, which is rare in paleoparasitological studies.Limitations: We were unable to acquire samples from cesspits dating to the 14th century.Suggestions for further research: Additional data from other Low Countries towns may strengthen the patterns identified in this paper. A similar approach can be used to investigate towns in different regions of the world.