Just came across this... Rome is in modern Italy so therefore the Romans came from Italy and I know the Romans built a "wall" in Africa which acted as a trade barrier. I wonder if Suella is confused.
Fossatum Africae. Fossatum Africae ("African ditch") is one or more linear defensive structures (sometimes called limes) claimed to extend over 750 km (470 mi) or more in northern Africa constructed during the Roman Empire to defend and control the southern borders of the Empire in Africa.

Might this have been the catalyst to Suella's little outburst?