WI Gunpowder is developed in the 3rd century BC in rome
I'm not sure the Romans would've appreciated the potential of something entirely new. Their age wasn't renowned for innovation. But let's suppose they made full use of it (perhaps bombs hurled by catapults). It would've made Roman domination of the Mediterranean easier, but basically things would still go as in the OTL. It's not like they really needed it, and the fall had little to do with technology.
Mining and other projects that require digging, as well as grading for roads gets a whole lot more interesting if the Romans have gunpowder.
Yeah, I can easily imagine Roman engineers squeeing with joy when they realize that they can now blow apart mountains.
Then you will have someone to think that if it breaks apart mountains then it would easily crush enemy cities' walls.
The fall was so far in the future that centuries of technology could have made a difference.
Walls too. Defenders fight back but this did not stop ancient soldiers from using rams, ladders or siege towers.
What centuries of technology? There was little technological progress in that era, and the accidental discovery of gunpowder wouldn't cause any.
!3C China had gunpowder but that didn't save them from the Mongols. The Ottoman Empire had it from the 18C at latest, but it didn't cause them to progress technolgically in any other way.
Bomb, smokes, flares, primitive rocketry like the Chinese had, yes. But no guns yet. Guns require steel good enough to make barrels that won't explode in your face, and a powder refined enough so a small charge can propel a bullet. That's two entire chains of technology that need to be mastered first and it won't happen overnight.
However, the military advantage won't last very long before other Mediterranean civilizations crack the secret of black powder too (as pointed out by Atamolos). Roman can still prevail, but through superior soldiering as they did OTL, not just thanks to new toys.
A few centuries down the line, advance in metal casting permitting, the first bombards and cannons may appears. But as much as I'd like to see Attila cut down in a artillery barrage, it is more likely at that point that butterflies would have already made the world unrecognizable.
However, the military advantage won't last very long before other Mediterranean civilizations crack the secret of black powder too (as pointed out by Atamolos). Roman can still prevail, but through superior soldiering as they did OTL, not just thanks to new toys.
A few centuries down the line, advance in metal casting permitting, the first bombards and cannons may appears. But as much as I'd like to see Attila cut down in a artillery barrage, it is more likely at that point that butterflies would have already made the world unrecognizable.
Not walls, but cities and fortifications usually have garrisons that like to fight back, what I want to point out is that using gunpowder against a wall involve more than what people think at first, the only practical way to use a charge against a wall is making it explode inside the wall or under the wall, exploding outside and above ground will make little damage. As posted by @MrGreyOwl guns aren't a given too. That makes gunpowder a lot less revolutionary as a siege weapon.
What would have been the impact if Rome's enemies managed to either gain access to the discovery of gunpowder or even managed to precede the Romans in discovering and effectively using gunpowder in battle?
Assuming that Attila himself didn't have cannon.
After 378 the Visigoths were stymied by not having the siege engines needed to take fortified towns. By 451 Attila's Huns did have them. These things don't stay secret.
Once gunpowder is widely used by siege weapons, city walls become moot. Walled cities were pretty much the only thing keeping the empire afloat during the late 4th century, so I suspect that the migration period would have been much more disastrous earlier than IOTL
Why not? You are interjecting a change the first century BC.
That's the point. You can't predict the thought processes that might be triggered over a period of centuries. You won't see guns very soon, but there would be an interest to advance metallurgy. By 200 AD, the world would be different. Gunpowder technology would, for sure, spread. But as it spread, armed warriors would have a distinct advantage over the unarmed. You are changing some of the most important years of Roman history.
But why should stumbling on the formula for gunpowder change anything else in particular? There was no scientific method in those days, so it could be found only by a fluke. There would be no reason for it to cause any other technological change. Greek Fire didn't when the Byzantines discovered that.
1. Ancient Mediterranean civilizations had excellent bronze casting skills (a couple tons in a single pour for larger naval rams, which had to be custom fitted to the ships timbers and able to withstand incredible impacts), so they could make good artillery without too much trouble.
2. Muskets are generally made with plain wrought iron, not quality steel. Moreover, the Romans did have access to quality steel through Noricum.
No, the design of city walls will just adapt. Lower and thicker, better overlapping fields of fire, shock absorbing materials, glaces, etc. I personally doubt migrating peoples would have the technology to cast hundreds of pounds of bronze without control of the urban centers the Romans monopolized by the first century.
Deleted member 90563
Someone would at least try to make the Roman equivalent of Mt. Rushmore, in the Alps.
Bastion forts, a millennium and a half earlier.
Bastion forts, a millennium and a half earlier.