"In a city of Nuremberg (Germany) in 1373 the first mirror manufacturing plant was open. Mirrors were then aggressively integrated in all aspects of life. In the 16th century mirrors become a part of mysterious rituals and witchcraft. Also, for 200 years mirrors were used by Spanish and French spies for coding and decoding secret messages. This secret coding system was introduced in 15th century by Leonardo da Vinci. The scriptures were coded in "mirror reflection" and without the mirror it was impossible to read the message. Mirrors were part of another big invention of the time - the periscope. The opportunity to discreetly spy on ones enemy by using a system of interactive mirrors saved a lot of lives during wars. During the famous Thirty Year war, mirrors were used by all sides to blind the enemy during military actions with bright reflection of sun light. It was very hard to take aim when your eyes are blinded by thousands of tiny mirrors."
This is just an excerpt. Much more to read. Link here.