The primary cause of the Great Fire of London in 1666 was a small fire that ignited at Thomas Farriner's bakery on Pudding Lane. The circumstances at the time, including dry weather and wooden buildings clustered closely together, allowed the flame to spread rapidly. The strong winds further exacerbated the situation, turning a manageable fire into a catastrophe that consumed a large part of the city. The fire lasted for three days, destroying thousands of homes, St. Paul's Cathedral, and major establishments. The aftermath prompted significant changes in urban planning, building regulations, and fire safety measures in London.