What led to the rise of the merchant class after the Punic Wars?

After the Punic wars and Carthage fell, its nearby rival Utica was made the capitol of the region and the leading center of Punic trade and leadership. Roman Empire was forced to rebuilt Carthage for the harbor was useless because of the accumulated silt from the grain cultivation in the Tunisian mountains that eroded the river. The fall of Carthage opened up a trading sea route as it is in the outlet of the Majardah river, Tunisia's only river which flowed all year long.