The year 1666 is most notably marked by the Great Fire of London, which began on September 2 and lasted for four days. The fire destroyed a significant portion of the city, including around 13,200 houses, St. Paul's Cathedral, and numerous other buildings. It is estimated that about 70,000 of the city's 80,000 residents were left homeless. In addition to the fire, 1666 was also a year of scientific advancement. Isaac Newton began his work on calculus and optics during this time, laying the groundwork for future developments in physics and mathematics. The year is often seen as a turning point in both urban development and scientific thought.