Travellers from the mainland, epicentre of the coronavirus outbreak , are required to keep themselves in isolation – quarantine – for 14 days after their departure from China , or contact with an infected person. Etymologically, the word “quarantine” stipulates a different number, 40, deriving as it does from the Italian quarantina ( giorni ), or “space of 40 (days)” – originally in the regional Venetian form quarentena – from quaranta (“40”), which is derived from the classical Latin quadraginta (“40”), tallied up from quattuor (“four”) and - ginta (“10 times”). While the practice of separating the sick from the healthy was noted in the Bible – in Leviticus, the third book of the Jewish Torah – the origin of the term “quarantine” stems from the time of the bubonic plague, or Black Death, which started in 1343 and spread devastatingly across continental Europe. The Great Council of the Venetian-controlled port city of Ragusa (now Dubrovnik, Croatia) passed a law in 1377 requiring that ships arriving from plague-affected areas be isolated for a month – 30 days – known as trentina , for “30”. This Venetian policy was swiftly adopted by other cities including Marseilles, Pisa, Venice and Genoa, the isolation eventually extending to 40 days (though in practice the number varied greatly). The clue to understanding this change in the period of isolation comes from two other, now obsolete, meanings of quarantine (earlier quarentyne), derived from the post-classical Latin quarentena and Anglo-Norman quarenteine : the place where Jesus fasted for 40 days; and a period of 40 days set aside or used for a specific purpose, as penance or service. Indeed, the 40-day Lenten fast preceding Easter, Jesus’ time in the desert and other Biblical 40-day trials, have a central place in the Christian world. Such established practices of 40-day periods of penance and isolation are believed to have influenced the shift to quarantina . Others suggest it stems from the Hippocratic belief that the 40th day distinguished acute diseases from chronic. Although quarantine was rarely applied in Britain and northern Europe, English writers borrowed the term from the mid-1600s, having observed the quarantina practice in Mediterranean ports (as did 18th century Arabic writers, as kurantina , observing it in Spain). By the late 17th century, in the Romance languages and consequently in English, “quarantine” extended to the isolation imposed on newly arrived travellers to prevent the spread of disease. Forty days or 14, quarantine is still used as a measure against an epidemic’s spread and, ultimately – per Cantonese 14 (sahp sei ) – “certain death”.