Interesting article about this: https://en.wikipedia.org/wiki/History_of_cannons

The oldest bell foundries do seem to happen at around the same time as the emergence of what we'd call a cannon, but before that there were indeed bamboo tubed contrivances and similar. If the Romans did have gunpowder earlier though, I bet they'd find a way.. I mean you don't hear about stone cannons and they'd be heavy AF but why not? These people basically invented fracking in BC, and literally tore down mountains to shake out all the gold. https://en.wikipedia.org/wiki/Las_M%C3%A9dulas