Back with another one-line wonder!

When a roman emperor tilted his head, he became nothing.

Why?

• Oh man - can someone point out which of the answers below came first? :/ – Mr Pie Nov 21 at 6:49
• You can sort by oldest. It was Deusovi. – Jay Nov 21 at 7:08
• @Deusovi by a whole 58 seconds! We must have both been writing up simultaneously (I was using a phone so did not get the push notification to say an answer had just been posted...). Formatting cost me... – Stiv Nov 21 at 7:19
• Enjoyed the one-liner, but I would recommend removing the extra commentary at the end, or if you must, writing it as a comment, since it isn't really a meaningful part of the puzzle – PiIsNot3 Nov 24 at 7:13
• @PilsNot3 ok, thanks for the advice. I’ll ensure that will happen in future - for now, I’ll reduct the extra commentary. Thanks for letting me know! :) – Mr Pie Nov 24 at 7:26

Because

the emperor is "Nero", and when the letter N is tilted sideways it turns into a Z, making it "Zero".

• It seems I have forgotten how clever the Puzzling community is, over the course of my absence. Well done ;) – Mr Pie Nov 21 at 6:50
• Congratulations, @Deusovi! $\color{green}{\checkmark}$ – Mr Pie Nov 24 at 7:30

The Roman Emperor is:

NERO

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')!

• Yes, that is correct - and very quick too! Great job! :P – Mr Pie Nov 21 at 6:51