But Alexandria is sitting by a vast river delta... vs Carthage especially and Rome which had centuries to develop the infrastructure to import from overseas. A river barge is much easier to build and control than sea going vessels. Besides- Carthage was never hugely populated, at least compared to some other ancient cities so 1 generation seems reasonanble. For Alexandria to surpass Rome in 20 years would be most questionable but not neceessarily in 100 years.