Medieval London was made up of narrow and twisting streets, and most of the buildings were made from combustible materials such as wood and straw, which made fire a constant threat. Sanitation in London was poor. London lost at least half of its population during the Black Death in the mid-14th century. Between 1348 and the Great Plague of 1666 there were sixteen outbreaks of plague in the city. In 1666, the Great Fire gutted much of London within the city wall.