There have been several speculations as to the cause of the Great Fire of Rome. One speculation is Nero started the fire so he could build a new palace. Nero couldn't have been playing a fiddle because they didn't exist. The bowed instrument wouldn't become popular for another 1000 years. Another speculation is a fire started in a house and spread throughout the city. When the fire was over 70% of Rome was in ashes. These are just a couple of speculations as there are more.