Complex sentence: Trade, shipbuilding, and banking helped support one of the largest and most powerful navies in the Mediterranean, but also famous and feared were the Genoese crossbowmen, (Mahdia campaign of 1087).
Split into simpler sentences: Trade, shipbuilding, and banking helped support one of the largest and most powerful navies in the Mediterranean. The genoese as well as skilled sailors were also feared warriors, remember the Genoese crossbowmen, and their exploits, (Mahdia campaign of 1087).