The Origin of “Quarantine”: Venice’s 40 Days at Sea

The word “quarantine” comes from the Venetian quaranta giorni — Italian for “forty days.” In the plague years of the 14th century, ships arriving at the great Adriatic ports were made to sit at anchor offshore for forty days before anyone was allowed to land, so officials could be sure the crew was not carrying the Black Death into the city. That waiting period became the word we still use today.

Where Does the Word “Quarantine” Come From?

The word “quarantine” traces back to quarantena, the Venetian dialect form of the Italian quaranta giorni, meaning “forty days.” It entered English in the 17th century, by way of the Italian quarantina, and it carried its original meaning with it: a fixed period of isolation imposed on people, animals, or goods suspected of carrying disease.

Before the word existed, the idea was already old. Societies had long separated the sick from the healthy — lepers were isolated in the ancient world, and the Book of Leviticus prescribed seven days of separation for skin disease. The first hospital in Damascus, built in the early 8th century, kept lepers apart from other patients. But none of these practices had a name, a fixed length, or a law behind them. The Black Death changed that.

Between 1348 and 1359, the Black Death wiped out an estimated 30 percent of Europe’s population. The plague arrived by sea, on trading ships from the Black Sea, and the great merchant cities of the Adriatic understood the danger with terrible clarity: every ship that docked could carry the disease into the heart of the city. They needed a system, and they invented one.

How Did the First Quarantine Law Work?

The first documented quarantine law in history was passed not in Venice but in its great rival across the Adriatic: Ragusa, the city-state we now call Dubrovnik, in Croatia. On 27 July 1377, Ragusa’s Great Council issued a decree with the Latin title Veniens de locis pestiferis non intret Ragusium vel districtum — “Those arriving from plague-infected areas shall not enter Ragusa or its district.”

The law required every ship and trade caravan arriving from an infected area to spend 30 days in isolation — a trentine, from trenta, the Italian word for thirty — on nearby islands, before anyone was allowed to enter the city. No citizen of Ragusa was permitted to visit the isolation area except officials appointed by the Great Council to care for the quarantined. Violators were fined. The city’s chief physician, Jacob of Padua, advised building a dedicated site away from the town for the care of suspected or confirmed plague cases.

It was a remarkable piece of public health law for the 14th century: written down, enforced by fines, and applied equally to everyone arriving from a plague port. And it worked. Ragusa’s approach became the model for every port in the Mediterranean.

Why Did Venice Make Ships Wait 40 Days?

Venice, the greatest trading power of the Mediterranean, followed Ragusa’s lead and then went further. In 1348, during the first wave of the Black Death, the Republic of Venice gave a council of three the power to detain ships and people in the lagoon. In 1374, a proclamation required ships from plague ports to wait on the nearby island of San Lazzaro until a special health council gave permission to enter.

Then, in 1448, the Venetian Senate prolonged the waiting period from 30 days to 40 days. That single change gave birth to the term “quarantine.”

The forty-day period proved remarkably effective. Modern estimates suggest the bubonic plague had a period of about 37 days from infection to death, so a forty-day wait was long enough for the disease to reveal itself in a ship’s crew. If nobody fell ill in forty days, the ship was almost certainly safe. It was, by accident or design, almost exactly the right number.

What Was a Lazaretto?

The waiting itself needed a place to happen, and the Venetians built one. In August 1423, the Venetian Senate ordered the use of a building on the small island of Santa Maria di Nazareth in the lagoon as a dedicated plague hospital — the first lazaretto. The word “lazaretto” comes from the island’s name, Nazareth, blended with the name of Saint Lazarus, the patron saint of lepers.

The Lazzaretto Vecchio, as it came to be known, was the world’s first permanent quarantine station. Suspected plague victims were brought there by boat, treated, and either released or buried on the island. Goods were unloaded, aired out, and sometimes fumigated with smoke before they were allowed into the city. A second island, the Lazzaretto Nuovo, was added in 1468 for ships and cargo. Dubrovnik built its own lazarettos too, and the model spread: Marseille adopted quarantine in 1383, and by the 18th century, every major European port had one. England passed its first Quarantine Act in 1710.

Why Forty Days — and Not Thirty?

Nobody knows for certain why the Venetians settled on forty days, and historians still argue about it. The leading theories are two, and both are plausible.

The first is religious. Forty is the great biblical number: the Flood lasted forty days, Moses spent forty days on Mount Sinai, Jesus spent forty days in the wilderness, and Lent lasts forty days. In a deeply Christian society, forty days would have felt like the natural, even divinely sanctioned, length for a period of trial and purification.

The second theory is medical. Ancient Greek medicine, following Hippocrates, held a doctrine of “critical days”: acute diseases were believed to reach their crisis and resolve by the fortieth day, which was regarded as the last day of ardent diseases and the boundary between acute and chronic illness. A forty-day wait, in this view, was the longest a disease could hide.

It is entirely possible that both explanations are true — that a medical rule of thumb and a sacred number happened to agree, and that agreement is what made the number stick. What is certain is that the forty-day rule outlasted the plague that created it, and the word built on it outlasted the rule.

How Did Quarantine Become a Global Word?

From the Adriatic, quarantine spread with trade. Every port city that wanted to keep trading without importing plague adopted the system, and the word travelled with the ships. By the 19th century, quarantine stations guarded ports from cholera and yellow fever as well as plague. In the 20th and 21st centuries, the word escaped medicine altogether: today we quarantine computer files, email attachments, plants, animals, and even spacecraft samples.

The word’s journey is a neat summary of its own story. A word born in a Venetian lagoon, built on a forty-day wait, now describes any period of careful separation before something new is allowed in. The ships are gone. The forty days are gone. The word remains — because the idea behind it, that you wait and watch before you let something in, never went away.

Frequently Asked Questions

What does “quarantine” literally mean?
“Quarantine” comes from the Venetian quaranta giorni, meaning “forty days.” It refers to the forty-day isolation imposed on ships and travellers arriving from plague-infected ports in the 14th and 15th centuries.

Which city invented quarantine?
Ragusa (modern Dubrovnik, Croatia) passed the first documented quarantine law in 1377, requiring 30 days of isolation. Venice extended the period to 40 days in 1448, which gave the practice its name.

Why was the quarantine period 40 days?
Historians offer two leading explanations: the biblical significance of forty days (the Flood, Moses on Sinai, Lent), and the ancient Hippocratic doctrine of “critical days,” which held that acute diseases resolved by the fortieth day. The forty-day period also closely matched the plague’s course from infection to death.

What is a lazaretto?
A lazaretto is a quarantine station, usually on an island, where ships, crews, and goods were held and inspected before being allowed into a port city. The first was established by Venice in 1423 on the island of Santa Maria di Nazareth in the Venetian lagoon.