When was the French door invented?

French Doors were popular in French architecture during the Renaissance period in the 17th century. However at first they were not doors at all but Windows instead. They were window casements that extended to the floor as this allowed more natural light to flood into the room. This was important as it was in the days well before electricity was invented. Apart from natural light, candle light was the only other form of light which only offered minimal light and in those days candles were expensive. Therefore the more natural light which you could get into a room the better.

French Doors were not used on the ground floor but were actually used on the first floor in buildings and would open up on to small balconies. It was not until the late 17th century that they were introduced into English architecture. As technology moved on doors became bigger and more elaborate.