Archimedes’ Mirror(s)

According to historians, Archimedes [A famous inventor] created a mirror[s] that deflected the sun’s rays and used them to burn ships of the invading Romans. Modern reenactors try to recreate it, but they can’t make it work at the range of 100 feet what was the range according to historians. There could have been more than one mirror. The first account of a mirror was 800 years after the siege of Syracuse! Do you think it is a myth?