of people into or out of a defined geographic area, such as a community, in order to prevent an infection from spreading. History Ancient An early mention of isolation occurs in the Biblical book of Leviticus, written in the 7th century BC or perhaps earlier, which describes the procedure for separating out people infected with the skin disease Tzaraath. The medical nature of this isolation is, however, disputed. As traditional exegesis (dated 700 CE) sees it as a punishment for trespassing one of several negative commandment, most notably Evil Speech. A more recent hypothesis postulates that the infected are required to isolate themselves in order to prevent spread of disease (although the Bible does not imply contagiousness of Tzaraath): Moses ordered that dwellings from which infected Jews had gone should be inspected before being occupied again, and that people recovering from contagious disease were not to be allowed to go abroad until examined. Medieval Islamic world A hadith attributed to the Islamic prophet Muhammad advised individuals present in a region with a plague outbreak to remain in place, and advised healthy individuals to avoid traveling there. The Persian Muslim polymath Avicenna argued for controlling “the spread of diseases" in his medical encyclopedia The Canon [Al-Qanun] of Medicine, published in 1025. He also recommended quarantine for patients with infectious diseases, especially tuberculosis. Since the sixteenth century, the Ottoman empire has isolated travellers coming from epidemic areas during the Bubonic plague. A quarantine involved isolating healthy travellers for a period of time so that it could be ascertained if they were sick or not. The mandatory quarantine of special groups of patients, including those with leprosy, started early in Islamic history. In the early 8th century the sixth Umayyad caliph Al-Walid I segregated lepers from the general population, with some later sources crediting the caliph with opening a hospital. The separation of lepers from the general population was also practiced in the Moroccan city of Fez, where lepers were relocated to a cave system outside of the city. Dedicated leprosariums were built in the time of the Ottoman sultan Murad II in the 15th century, with some of the facilities operating for centuries. Medieval Europe The word "quarantine" originates from quarantena, the Venetian language form, meaning "forty days". This is due to the 40-day isolation of ships and people practised as a measure of disease prevention related to the plague. Between 1348