Watch on Soap2day. Chambord, the most impressive castle in the Loire Valley, in France, a truly Renaissance treasure, has always been an enigma to generations of historians. Why did King Francis I (1494-1547), who commissioned it, embark on this epic project in the heart of the marshlands in 1519? What significance did he want the castle to have? What role did his friend, Italian genius Leonardo Da Vinci (1452-1519) play? Was he the architect or who was?