Since antiquity, with the growth of the human population and the expansion of nuclei of people (aggregations), infectious diseases have been a constant presence which decisively changed the course of history. The word "lazaret", meaning hospital for the hospitalization and treatment of plague victims and later, also leprosy, is Venetian. It was coined in the 14th century, and was exported to the world; it is still in use although it has slightly modified its meaning: "hospital in general, and shelter for infectious diseases". Lazarets perhaps arose from the overlapping and crossing of the name Nazareth associated with Lazarus, protector of leprosy patients and from other contagious diseases in general. The island of "Lazzaretto Vecchio", overlooking the Lido di Venezia, was named Isola di Santa Maria di Nazareth before the 15th century. However, the first city to take an official step in this direction was the Republic of Ragusa (Croatia), a city-state and flourishing Maritime Republic which was a trading pivot between the Ottoman Empire and the West. In 1377, for the first time in history, the city established a thirty-day quarantine on the three uninhabited islands of Mrkan, Bobara and Supetar for people arriving from infected places. The Republic of San Marco (Venezia) devised one of the oldest and most far-sighted sanitary solutions to contain the spread of the plague: a lazaret, or sanitary model of isolation and treatment that spread, with the name radiating from Venice, around the world. Venetian lazarets were the site of the Republic's innovative strategy to prevent and combat the plague, not only by isolating people for quarantine and goods from infected countries, but also by implementing complex procedures of 'contumacy and purgation' that required a constant investment of economic resources and slowed down traffic. Venice's governors quickly realized that spending money to prevent and fight the plague in lazarets was the only way to counter the economic and demographic collapse caused by epidemics. In the wake of the Venetian and Ragusian lazarets, Trieste also established its first lazaretto in 1717. This was because ships laden with goods from the Near East began to arrive in the city, and this new situation necessitated the adoption of a regulation of contumacy and the construction of a lazaret. This study aims to bring light to the main lazarets over the centuries, particularly those in the Ferrara district and those located in the upper Adriatic Sea, such as Trieste and other neighbouring cities built to fights pandemics.