Genetic analysis of DNA from victims of the Black Death, exhumed from archaeological sites in Estonia, Russia, England, the Netherlands, and Switzerland, has shown that the plague did not vanish after its initial outbreak between 1347 and 1353. Instead, the disease was reintroduced multiple times over four centuries, with a notable increase in new genetic versions of the bacterium Yersinia pestis around 1450. These findings, published in the journal PNAS by researchers from the University of Tartu in Estonia, challenge the traditional belief that the Black Death was a single, isolated event. The study reconstructed 26 complete genomes of Yersinia pestis from skeletons found at 11 archaeological sites, spanning the 14th to the 18th century. Researchers used radiocarbon dating and cross-referenced these measurements with the position of each strain in the bacterium's genetic tree, as well as local historical records, to accurately date the genomes. This method allowed them to redate 75 previously analyzed genomes. The analysis identified a key turning point between 1450 and 1500, during which the bacterium split into three major genetic branches. This suggests the emergence of new sources of the disease in wild rodents, challenging the previous idea that a single source had fueled the plague in Europe since 1347. The researchers proposed a climatic explanation, noting that the Great Drought of the Renaissance coincided with this period. Recent studies also suggest that climate changes can influence plague outbreaks in rodent populations. Estonia provides one of the best-documented examples of repeated Black Death outbreaks. The country experienced multiple introductions of the disease from the end of the 14th century, both in cities and rural areas. The presence of new genetic lineages in Estonia suggests that its commercial connections with the rest of Europe helped spread the disease repeatedly. The spread of the disease was not only due to commercial activities. The newly analyzed genomes show outbreaks during the Thirty Years' War (1618–1648) and the Great Northern War. Armies, refugees, and merchants played a significant role in moving the bacterium across regions. For example, during the siege of Tallinn in 1710, the plague affected Swedish soldiers, Russian soldiers, and civilians. Although the Black Death has long been absent from Europe, Yersinia pestis continues to exist in wild rodent populations on several continents, with a few human cases reported each year. Modern antibiotics effectively treat these cases. Understanding the historical spread, persistence, and eventual decline of the plague in Europe can help monitor the still-active sources of the disease today.