In 397, Dionysius assembled a huge army of 80,000 men and a navy of 200 ships and sailed toward the western apex of Sicily, the stronghold of the Carthaginians.  He captured Eryx and then attacked Motya, a strongly fortified city on an island in the large harbor.  As the Greek forces approached, the people of Motya destroyed a causeway linking the island to the mainland.  Undeterred, Dionysius ordered his men to build a mole, a land bridge, to the island to replace the causeway.  They did so, and brought up wooden towers six stories high, on wheels, to attack the lofty walls of the city.  This was the beginning of massive siege engines that would threaten walled cities later in the fourth century.  Dionysius also prepared catapults to throw stones from a distance, the beginning of siege artillery.  Motya eventually fell, and the Greek troops massacred the inhabitants. 

            The following year, the Carthaginians sent an even larger expeditionary force of 300,000 men and 400 ships, led by Hamilco, to counter the Greek invasion of their territory.  He recovered the Eryx and destroyed Motya, building Lillybaeum nearby.  With his support, the Sicels of Naxos, whose city had been destroyed by Dionysius, built Tauromenium on the cliffs above the east coast of Sicily.  Hamilco’s armada sailed to Syracuse and captured the Great Harbor, setting up camp in the swamps on the northern shore, initiating a siege of the city.  Suddenly a plague devastated the Carthaginians, presumably mosquito-borne malaria.  As the plague was doing its damage, Dionysius attacked the Carthaginians by land and sea, killing many soldiers and sinking ships by ramming and setting them afire. 

            Dionysius could have finished off Hamilco and the remaining forces, but he took a bribe, reportedly of 300 talents, from the general.  Dionysius kept his forces from attacking while Hamilco and the Carthaginians (not including Sicilians and Iberian mercenaries) escaped during the night.  When Hamilco returned home the Carthaginians revolted against him and he took his own life. 

            In 393-392, Mago, who had commanded Hamilco’s navy, attacked the Greeks in an attempt to win back their former territory.  Dionysius in league with Sicel leaders defeated him and made a new treaty, this time giving Dionysius the rule over the Greek states of the island, and also over the Sicel nation.  Dionysius was also given control of Tauromenium, which thus far had held out against him.