The engine suddenly 'roared (back) to life'. [=it made the loud sound of an engine and began running well]
The audience 'roared' with laughter. [=the audience laughed loudly for a long time]
The fans were 'roaring' [=yelling and cheering loudly] after their team scored.
(..) I think he knows what Rome is. Rome is the mob. Conjure magic for them, and they'll be distracted. Take away their freedom and still they'll roar. The beating heart of Rome... is not the marble of the Senate. It's the sand (..)2000 Gladiator