On September 5th 1666 the Great Fire of London was finally extinguished.
The fire started at a bakery on Pudding Lane on Sunday 2nd September. A drought that had affected the city since November of the previous year had caused many of the wooden buildings to become dangerously dry. The three day fire gutted most of the old medieval city that was within the Roman walls - what is today the City of London - destroying the homes of an estimated 70,000 of the 80,000 inhabitants. The death toll is unknown; it was originally thought to be only six, as those are the verified deaths, but many deaths may not have been recorded (they were nobody important) and the fire would have destroyed the bodies.
On the plus side, the fire appeared to have stopped the plague (the Black Death). The previous year was known as the Great Plague, estimated to have killed a sixth of the inhabitants, and the plague did not occur again after the fire.
Image: See page for author [Public domain or Public domain], via Wikimedia Commons