[Graymatter]

Also, a lot of the archaeological sites are either underwater or hopelessly silted over. Agde in southern France comes to mind. What the water and the silt didn't get, the pirates, the Carthaginians, the Romans, and the Vikings messed with. Then the builders of the Canal du Midi. Then the modern day resort developers. Good luck finding a trace of the old trading port now! And there were dozens more like it.

[Heatseeker]

All this applies to Carthage as well. Between the Romans, the Byzantines and the Muslims, we would know next to nothing about it, were it not for the preserved classical writings.

At the risk of being foolish by stating the obvious, a lot of it is merely the passage of time. Massalia/Marseilles was founded about 600 BC and its glory days were long gone when the Romans showed up.