In late autumn 2006 archaeological excavations were undertaken in St. Gertrude’s churchyard in Riga. 719 burials including two mass graves were uncovered. The most extensive use of the cemetery was during the 16th to 17th centuries. A nthropological analysis determined that inhumations in the mass graves might contain inhabitants of Riga or refugees who had died from disease and/or famine. Analysis of soil mineralogical composition indicated that dolomite limestone (CaMg(CO3)2) was probably used to disinfect the bodies of epidemic victims in one of investigated mass graves .