Successor State + Carthage 'What If?' Question

[Watchman]

But there was a limit to the amount of slaves that could be employed, as they required food, they were expensive, and most importantly, they needed guarding. With a steam engine, you don't have that third problem, something which ancient nobles might have seen.

...except all that and then some applies to the people who run the machines as well. Not only do you still need the blue-collar grunts to do the heavy lifting; you also have the engineers, technicians and whatever who keep the gadgets operational - and, not being exactly easy to replace, the latter can readily ask for some pretty salty wages and perks indeed...

Indeed, but Gaul had forests, Britannia had coal, and Germania had lots of forest.
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It depends on the location. Arabia? Of course not. Germania? You're surrounded by fuel.

And all those are in the periphery insofar as the Med - the true heartland of the Classical civilisations - is concerned; Germany indeed was pretty much a no-go anyway, as it couldn't even produce enough of a consumables surplus to allow the Romans to permanently garrison an army there (and, hence, have a realistic shot at conquering it).

Wanna start adding the shipping costs to the fuel bill ? That's not going to make it any more attractive to thinkers in the Mediterranean metropolises, all the more so as rather expensively imported wood was already direly needed for God knows how many other things...

I've been thinking about it, and I think that would have proved to be the biggest obstacle. It depends on the nature of the engine, but I don't we'd have seen massive Romani liners/steam tanks in the first century or two. However, if people had realised the potential behind steam power, they might have been inspired to experiment with metallurgy techniques, and certainly, had the Empire as a whole realised that, then I think technology could have advanced quite quickly.

Uh-huh. What you're describing is more or less the "scientific principle" paradigm of problem-solving. Too bad it doesn't actually work that neatly IRL, and moreover lay well over a millenia in the future during the heydays of Rome...
We're not talking about Civilization here; people didn't just sit down and go "hey we need better metallurgy, let's invent it - oughta take a century or two"; plus, what do you think the High-Late Medieval breakthroughs in metal reduction techniques, furnace construction, actual smithwork etc. were the product of if not millenia of continuous trial-and-error developement and hands-on experimentation ? And that was a long stretch of busy centuries indeed from where the Romans stood, with no small amount of helpful imported influences to boot which AFAIK were yet to be accessible in Antiquity.