What natural disaster would destroy a Roman era empire in a short time?

I would choose an earthquake. It will give greatly impact to the empire.Those natural disaster you mentioned above will greatly give impact to it but I will choose earthquake as it can get it down in a minute. If it through war for example it will take years to find other empire to defeat them.(^^)

It'd take something massive to physically destroy an entire empire - maybe a meteor hit that completely eradicates an entire part of the world. That'd also do enough damage to wipe out any communication links and leave enough people stranded from the capitol that the administrative structure would fail, especially if they were using local military/civil governors. Those local people who survived would just go it alone, since (assuming the Roman model) they'd have military backing from the local militia/guard. Alternatively, a single-location disaster could wipe out the capitol: tsunami, earthquake, firestorm, volcano, even rabid animal invasion. If the entire administrative function of the empire was centred in the capitol, that could be enough to loosen their grip on surrounding territories and allow the subjugated locals breathing room for an uprising, external enemies to seize the opportunity to invade or general civil unrest through fear to take over. One of the best natural disasters (for destroying an empire) is plague. People are so scared that ANY external influence - religious, political or otherwise - can take advantage of it and totally dismantle an empire if they move in quick enough and build influence amongst the afflicted.

Well, the empire could be destroyed by multiple volcano's erupting and covering the area with lava and ash. An extremely large earthquake could also cause enough damage and fear that people might not be willing to stay in the area any longer. No people, no empire. Okay, those are my ideas. I hope it helps you.

A big tidal wave, earthquake, nova, or something like this. I was just watching on the History Channel about that area and they were talking about a tidal wave. What about a Psunami? Or a collection of things. One causing another to happen and then a fire to finalize things.

I think it could be a flood, because all people would drown rapidly and force of water could destroy all the buildings. If it's valid to mention another one, I would tell you a vulcanic eruption like that of Pompeii. In such case would be difficult for anyone left alive.

Mine would be an earthquake. It can level cities, kill people and create a psychological shock to the survivors. Then again, a meteor is even greater. Fast and efficient, depending on the size of the meteor, I imagine that the impact would be as strong as that of an atomic bomb.