On this date in 1666, the Great Fire in London began and ravaged the city until September 5. Almost all of the city's inhabitants were left homeless. The city was a giant firetrap, with most structures made of wood with fires going inside. The fire actually started at a bakery, and then spread unchecked to consume much of the city.
Fire fighting methods were limited in those days. Essentially London had a local militia that relied on water they could carry and demolition to control fires. Creating fire breaks by pulling down structures was exceedingly common, and many historians think that liberal use of this method was what eventually won the fight against the Great Fire.
The city lay in ruins and even the king, Charles II, suggested settlement elsewhere. In time, however, all proposals for movement or restructuring were abandoned and the city was rebuilt in essentially the same way as before.
It is exceedingly difficult to gauge the cost of the Great Fire in terms of lives lost. Most official reports placed the number in the single digits, but these probably ignore direct losses to the poor inhabitants and ancillary losses after the fire. Many people may have been incinerated by the blaze, or perished later due to smoke inhalations; further, many people probably died in makeshift camps constructed to house people afterwards.
So there's a happy thought for you.