[SpringheelJack]

As I recall, Crassus had molten gold poured down his throat, as a mockery of his wealth. Beheading would have been kinder.

Not while alive though. IIRC, he was killed after the battle when a truce negotiation went bad.

[SunkenCiv]

"a truce negotiation went bad"

That's a polite way of saying, the Parthians said they'd negotiate the surrender, then violated the truce and slaughtered everyone they could get their hands on.