This research, examining the site of the HKP Forced-Labor Camp in Vilnius, Lithuania, located and better defined the characteristics and remaining features of the 1944 camp. There were four over-arching objectives for this research. First, to find the entrance into the principal hiding place where Jews interned in the camp took refuge just before the camp’s liquidation by the Nazis and their local collaborators. Next, find the location of the burial trench(es) where Jewish prisoners who were found in hiding were murdered and initially buried. Next, to find the mass-burial site where Jewish survivors reburied the remains from the trench(es). Lastly, to locate any other evidence related to the murder of Jews at the HKP 562 site. Ground-Penetrating Radar (GPR) found the principal hiding place in the basement of Building 2. Electrical Resistivity Tomography (ERT) discovered the two trenches where camp inhabitants who were shot on-site during liquidation were first buried. ERT also found the location of the mass grave that holds the reburied remains from the trenches. Bullet-scarred walls near the burial trenches indicate where the Jews were shot on-site. This research solved one of the thousands of unknowns about the Holocaust, using geoscience to uncover forgotten and hidden history. The materials and methodologies used in this research can be applied in uncovering this history at thousands of other Holocaust and genocide sites worldwide.

The non-destructive geophysical testing method ground penetrating radar (GPR), along with satellite image and air photo assessment, a review of the existing literature sources, and Holocaust survivor testimony, was used to document the location of potential mass graves in Alytus, Lithuania. In World War II, six million Jews were murdered, as were as many as five million other victims of Nazi Germany’s orchestrated persecution. In the summer of 1941, 8030 Jews (4.70 percent of Lithuania’s Jewish population) lived in Alytus County, where the town of Alytus is located. It is estimated that over 8000 Jews were murdered in Alytus County, including nearly the entire Jewish population of the town of Alytus. The murder of Jews from Alytus County accounts for approximately 4.2% of the total number of Lithuanian Jews killed in the Holocaust. Survivor testimony indicates that several thousand Jews from both the town and county were murdered and buried in the Vidzgiris Forest about 1000 m from the town center. In 2022, field reconnaissance at locations in the forest, which appeared to be disturbed in a 1944 German Luftwaffe air photograph, indicated that these disturbances were associated with natural geomorphic processes and not the Holocaust. Analysis of GPR data that was collected using a pulseEKKO Pro 500-megahertz groundpenetrating radar (GPR) system in 2022 in the vicinity of monuments erected in the forest to memorialize mass graves indicates that no mass graves were directly associated with these monuments. The 1944 air photograph contained two roads that traversed through and abruptly ended in the forest, which was the impetus for detailed field reconnaissance in that area. A segment of a 150 m long linear surface feature found in the forest was assessed using GPR, and based on the profile that was generated, it was determined that this feature is possibly a segment of a much more extensive mass grave. Testimony of a Holocaust survivor stated that as many as three burial trenches exist in this portion of the forest. Additional research using non-destructive GPR technology, air photograph and satellite image assessment, and the existing literature and testimony-based data are required for the Vidzgiris Forest to better define these and other potential mass graves and other Holocaust-related features.

A common practice used by the Germans and collaborators in World War II, as part of the Holocaust, was to use existing Jewish cemeteries as places for mass burial. Research was completed at the Old Jewish Cemetery in Riga, Latvia, the Livas Jewish Cemetery in Liepaja, Latvia, and the Zaliakalnis Jewish Cemetery in Kaunas, Lithuania. The Old Jewish Cemetery in Riga was adjacent to the Riga Ghetto and was used to bury individuals murdered in the ghetto. In Kaunas, an area of the Zaliakalnis Jewish Cemetery is devoid of grave stones, and literature sources and testimony indicate that this area was used for the mass burial of Jews from the Kaunas Ghetto and other mass killings. In Liepaja, the local Jewish Heritage Foundation believes that there are mass graves within the Livas Cemetery. Methodologies for this research include the use of a pulseEkko Pro 500-megahertz ground-penetrating radar (GPR) system. Electrical resistivity tomography (ERT) data were collected through a linear array of electrodes coupled to a direct current (DC) resistivity transmitter and receiver. Analysis of aerial photography and satellite images was also employed at each location. ERT and GPR data indicate three separate trench anomalies in the Old Jewish Cemetery in Riga. The presence of these anomalies corroborates Holocaust survivor testimony that bodies were buried in mass graves in that area. In the Zaliakalnis Jewish Cemetery in Kaunas, ERT and GPR data indicate an anomaly in the western part of the cemetery, and ERT data further indicate two other possible mass graves. In Liepaja, preliminary GPR analysis indicates an anomaly in a cleared section of the cemetery. Based on the presence of geophysical anomalies in all three cemeteries, which correlate with literature sources and Holocaust survivor testimony, there is a high probability that mass graves are present at each site. Future research directions include expanding the search areas in each cemetery, additional literature and testimony-based research, and the addition of other geophysical methodologies.

Jacob Gens, the head of the Vilnius Ghetto Police Force, and eventually the entire Ghetto during the Holocaust, was murdered on 14 September 1943 by the head of the Vilnius Gestapo. Historical documents and Holocaust survivor testimonies indicate that he was killed at a site that became known as the Rasu Street Prison, and not the Gestapo Headquarters, as it is widely believed. In 2016, research was completed at the Rasu Street Prison site using ground penetrating radar (GPR) and electrical resistivity tomography (ERT) to locate subsurface reflection patterns that possibly indicate the location of where Jacob Gens is buried. Intersecting GPR and ERT reflection patterns were discovered and a plan was put in place to excavate that location. The excavation revealed the presence of human remains at 1.45 m below the surface. A skull and upper torso were exposed, and two teeth were collected for DNA and radiocarbon analysis. The DNA from the tooth was compared to Jacob Gens’ daughter’s DNA, and this comparison yielded a negative result, so the human remains were not those of Jacob Gens. The radiocarbon analysis provided a date between 1685 and 1735. In 1705, a plot of land was donated to the Visitation Monastery, which used this plot, and which coincides with the location of the Rasu Street Prison, as a cemetery for the poor. In 1709 and 1710, a plague epidemic was prevalent in Vilnius, as was turmoil and famine associated with the Great Northern War (1700 to 1721). Based on these discoveries, rather than finding the remains of Jacob Gens, it is likely that we found human remains that are part of a forgotten 18th century cemetery associated with the Visitation Monastery.

This study investigates the subsurface remains of Jaundole Castle, a 14th-century medieval fortress located on Dole Island near Riga, Latvia. The castle, which has left no visible surface ruins, is known only from historical documents and maps. To assess whether its buried remains could be detected, a non-invasive ground penetrating radar (GPR) survey was carried out across five targeted grids. The results revealed multiple linear and circular anomalies consistent with historical records of the castle’s layout, including possible foundations of walls and towers. These findings demonstrate that GPR, when combined with historical map and image analysis, can effectively locate, and delineate lost architectural features. The integration of historical sources and geophysical data provides a replicable model for the investigation of other completely buried archaeological sites. This work contributes to the development of non-destructive prospection strategies and supports the planning of future archaeological excavations and conservation actions.

The geophysical techniques ground penetrating radar (GPR) and electrical resistivity tomography (ERT) are commonly used data collection methodologies in numerous disciplines, including archaeology. Many researchers are now, or will be in the future, associated with projects that use these geophysical techniques, but who are not well versed in the instrumentation, its function, related terminology, data interpretation, and outcomes. This entry outlines the general approach and background for completing this type of research, dissects the methodology from a completed geoarchaeological project that uses both GPR and ERT, and provides concise definitions and explanations for all facets of the methodology. Based on this methodology, 21 terms or concepts related to GPR are explained in detail, as are 26 terms or concepts related to ERT, and visual representations of some of the terms and concepts are further illuminated via 11 figures. There are also 133 references linked to the various concepts and terms presented in this entry.