The
Latin name for the po
river was
"padus", and the plain that it traverses came therefore to be called
Pianura Padana (meaning the padus plains).
Recent bizarre twists in Italian politics have given unsuspected undertones to the shorter Padania (which used to have the same meaning as above), which is now best avoided as a simple toponym.
The Po river used to act out quite a bit, thus giving lots of problem to the neighboring areas, which appeared to be spending about as much time underwater as above. Works conducted in the second half of the XX century appear to have tamed the old man river a bit, however.