On 17 March in the 17th century (the exact year is not consistently recorded in surviving sources), London authorities carried out an enforcement of quarantine measures during a plague outbreak. The action fits within a pattern of civic responses that intensified across the century as city officials, parish constables and health commissioners sought to limit contagion through isolation, movement controls, and localized closures. Context Plague recurred in London repeatedly during the 1600s, with major outbreaks in 1603, 1625, 1636, and the catastrophic Great Plague of 1665–1666. Public-health responses drew on earlier medieval practice and emergent municipal regulations: infected houses were marked and sealed, victims and their close contacts were confined, markets and theatres could be closed, and watchmen or constables were tasked with enforcement. These measures were unevenly applied and their documentation varies by parish and year. What the 17 March record shows Surviving parish records, municipal orders, and contemporary diaries occasionally note specific enforcement dates. An entry citing 17 March refers to orders to prevent egress from infected houses and to ensure watchmen guarded streets where infections were suspected. The notation indicates authorities undertook actions to isolate households and restrict movement—core elements of quarantine enforcement—rather than merely issuing advisory warnings. Implementation and actors Enforcement typically involved several local actors: parish clerks and churchwardens recorded and reported sickness; constables and watchmen carried out closures and guarded doors; searchers (often women paid by parishes) certified deaths and causes; and city officials or commissioners issued overarching directives. Households ordered to be shut up were often supplied minimally by parish relief but could also be subject to fines or other penalties for breach. Records suggest the 17 March enforcement would have reflected this patchwork system of responsibility. Limitations and sources The precise year attached to a 17 March entry is not consistently extant in all sources; some surviving documents omit the year, others use regnal or ecclesiastical dating conventions that require cross-referencing. Because contemporary documentation is fragmentary and sometimes inconsistent across parishes, historians treat single-date entries cautiously and place them within broader outbreak chronologies using corroborating evidence (bills, diaries, corporation minutes, and burial registers). Impact and significance While a single enforcement action on 17 March cannot be taken as evidence of a coordinated citywide strategy, it exemplifies how 17th-century London enforced isolation at the household level. These measures shaped daily life: households could be shut up for weeks, contact was limited, and economic and social routines were disrupted. The enforcement practices of this period also influenced later public-health approaches by demonstrating both the potential and the social costs of quarantine. Conclusion The 17 March enforcement record captures a representative instance of early modern quarantine practice in London: localized, parish-driven, and reliant on a patchwork of civic actors. The absence of a consistently recorded year in some documents means the entry should be read alongside other sources to place it precisely within the chronology of London’s plague years.