Quarantine as filter: a conceptual framework from early modern Venice.

Lazzaretto Vecchio, founded in 1423 in the Venetian lagoon, is recognized as the earliest permanent quarantine hospital. For nearly three centuries it operated at a major maritime frontier. Historical records describe extensive epidemic mortality and mandate burial on quarantine islands, leading to the long-standing model of a Venetian plague house dominated by resident burials (H1). Yet the island's physical capacity is insufficient to accommodate all documented epidemic deaths, exposing a persistent discrepancy between archaeological evidence and early modern narratives of epidemic containment. Here, we synthesize historical, archaeological, and demographic evidence and argue that the available evidence does not support the interpretation of Lazzaretto Vecchio as a comprehensive cemetery for Venice's epidemic dead. Instead, the burial assemblage is most consistent with selective demographic filtering associated with quarantine practice. We present two complementary explanatory models: (H2A) the Ellis Island Effect, dominated by intercepted travelers; and (H2B) the Secret Republic Fire, in which peak urban mortality was diverted through undocumented crisis disposal. Together, H2A and H2B describe a dual-regime containment system most consistent with the available evidence. By reframing quarantine as an active filtering process rather than a passive repository of epidemic mortality, this perspective highlights how governance and infrastructure shaped the burial record and created a unique opportunity to reconstruct infectious disease diversity and evolutionary trajectories across three centuries.