When a roman emperor tilted his head, he became nothing.
the emperor is "Nero", and when the letter N is tilted sideways it turns into a Z, making it "Zero".
The Roman Emperor is:
When he 'tilted his head', he:
Rotated his initial letter by 90 degrees. Thus 'N' became 'Z'.
Thus making him become:
ZERO (i.e. 'nothing')!