The straits of Gibraltar never quite opened and the entire Mediterranean basin is dry land apart from a few large salt water lakes at the lowest points ~5% by area. The Europe – Africa land bridge has been slowly eroded and is now just 2 kilometres wide and no more than 10 meters high at any point.
It is April 100 AD and a civilization similar to that of Rome holds sway over the lands of the Roman Empire and the whole of the Mediterranean basin. A particularly high and fierce storm tide temporally breaches a one kilometre stretch of the centre of the bridge allowing a little salt water in and reducing the barrier height to just 1 meter above normal high tide level before retreating again. The recent breach is the first sign of the seriousness of the situation. The composition of the land bridge is a simple extension of the coastal rock on either side of the straights as we know them.
Would a civilization similar to that of Rome have been able to understand the danger they faced and be willing and capable of taking effective action to prevent catastrophe over the short and long term?
Out of scope
Any arguments about the Roman Empire not being able to evolve without the Mediterranean sea. History would have been very different but it’s there.
No magical involvement.