This study presents my second major attempt to make historical sense out of the new evidence emerging from phylogenetics and paleogenetics about the proliferation of Yersinia pestis (the bacterium that causes plague) in late medieval Eurasia and Africa. My first attempt, “Putting Africa on the Black Death Map: Narratives from Genetics and History,” Afriques 9 (24 December 2018), http://journals.openedition.org/afriques/2125, examined the trajectory of a newly formed lineage of Y. pestis, 1.ANT, asking how a strain of plague that was known to have been involved in medieval Europe could have ended up in modern East Africa. That, in other words, was an “aftermath” question. The present essay, “The Four Black Deaths,” instead looks at the evidence for what happened before the Black Death, as it is understood from European sources (both historical and now genetic). I argue not simply that the genetic evidence is very clear in supporting a “Big Bang” of plague proliferation (so-named and first described by Cui et al. 2013), but that the geolocation of closely related surviving strains place that “event” somewhere in or near the Tian Shan mountains, which lie at the border between Kyrgyzstan and China. Genetics could only offer a “window” in which this event occurred in historical time. I present evidence that might plausibly pinpoint when one product of the Big Bang, Branch 1, moved westward during a peak phase of the expansion of the Mongol Empire. The Supplemental file collects the evidence for Big Bang strains of plague in various marmot populations. For subsequent work that expands on these arguments, see Joris Roosen and Monica H. Green, “The Mother of All Pandemics: The State of Black Death Research in the Era of COVID-19 – Bibliography,” 30 August 2023, Humanities Commons, DOI: https://doi.org/10.17613/57tg-sz07.