|The Decline of the Carthagian Empire, JMW Turner; Tate Britain|
...Except that it did grow back. Not immediately of course, and only because the Romans allowed it to. The New Carthage was founded by Julius Caesar in the years before his demise. But Utica, the Roman ally which was appointed the new capital of Roman North Africa, was soon overshadowed, and the new Carthage soon became once again the greatest city in North Africa - indeed one of the greatest cities of the Western Roman Empire. What was it about this location which made it such a natural site for great cities?
The answer, I believe, comes from two things: first, a look at a map of the Mediterranean, and second, some facts about ships of the ancient world.
Carthage, as mentioned, was in what is now Tunisia - notably, near the narrowest crossing of the Mediterranean (though still a solid 100 miles across the sea from Sicily). This was in an era when sailing ships might achieve 50-60 miles on a good day of sailing. Crucially, ships of the day had to take to land every evening in order to dry out the wood. This had a number of consequences: for example, ships would not carry more than a day or two's supply of food with them, but would instead land in ports and acquire food (2).
Consider what this means for journey times and possibilities. Journeys from the north of the Med to the south are obviously greatly shortened in many cases. But this also gives opportunities to sacrifice directness for security. Someone sailing from Algeria to Egypt has the option to avoid the less-populated, less secure Libyan coast, and instead to coast around the north of the Med through well-known trading waters.
(1) This could be an interesting debate in itself. In the recent Princeton University Press sale I eventually did end up buying Josephine Quinn's In Search of the Phoenicians, which argues - as best I can tell - that the Phoenicians did not exist as such, but rather that there were various seafaring people who were all given the same label. This would be a very plausible hypothesis, and deeply appealing to me as someone who wishes to emphasise the vast diversity of past societies which has been flattened out by modernity in general and capitalism, mass media, and nationalism in particular, were it not for a book I did get: Taco Terpstra's Trade in the Ancient Mediterranean, whose second chapter argues that long-distance trade in the Ancient Med was facilitated largely by the existence of Phoenician minority communities in cities around the Med. Trade relies upon trust, which would have been very difficult to achieve in the absence of enforcement mechanisms - except that local ethic Phoenicians were able to send messages back to Tyre and to other Phoenician colonies and obtain justice - and were obviously subject to the justice and tolerance of the local majorities.
(2) Thus, towards the end of the Peloponesian War, the Athenian fleet happened to be caught on the defensive near the home-in-exile of their former general, Alcibiades, perhaps the chadliest man in all of Classical Greece. Alcibiades advised the Athenians to move their pitch closer to the town, on the grounds that their sailors would then spend less time away from the ships buying food and other supplies; this advice was ignored, and the fleet was soon lost, definitely knocking Athens out of the war.