No. Neither them, nor the Romans, nor the Byzantines are responsible for that; and if you take into account that until the mid-15th century the Kingdom of Naples was among the most prosperous in the Peninsula, you can see why that affirmation can't be true. In reality, much of the South's disparities can be addressed to the rapacious Spanish domination (1516/1734), as well as the mostly inept rule of the Bourbons (who failed to turn the country into a modern industrialised State despite it being, ironically, on the forefront of many innovations).

Unification was beneficial from many points of view - however, despite the progresses, many of the old structures of power which had impeded the South's development were left at their places and this, coupled with the absence of an entrepreneurial class/spirit among the local elites as well as the competition from the industries up North (which the new unitary government hoped would provide some kind of stimulus) is why the South is what it is.

Also - 60 years of corrupt local governments, often under the banner of the Democrazia Cristiana, had their toll.

hi! you may be interested in earlier discussions on this

• Why has the South of Italy been so much poorer than the North throughout modern history, and why has it remained poorer during the 20th century?

• thread in Why are countries generally split politically, economically, socially, etc. along North-South lines?

• Why is there such a disparity between Northern and Southern Italy?

• Why is their such a big difference between northern and southern Italy?

• why is northern Italy so rich and southern Italy so poor?