Why did London have a big fire?

Answer 1

Houses are built mostly of flammable materials (wood, etc.) and they burn very easily, and fire spreads very easily from one house to another, especially in a crowded city. The only reason why cities are not always burning down is that we now have very efficient fire departments that put out fires before they spread. At earlier periods in history, London did not have an efficient fire department, or any fire department, so it was very vulnerable to fire.