0
From Tardis Wiki, the free Doctor Who reference
According to the Eighth Doctor, "round about 0 BC, AD", the first Christmas took place. He went to attend it with Leonardo da Vinci. (AUDIO: Relative Dimensions)
Behind the scenes
In the real world, in the common Western calendar, the year "zero" does not exist, with a direct progression from 1 BC to 1 AD.
