The siege of Syracuse by the Carthaginians from 311 to 309 BC followed shortly after the Battle of the Himera River in the same year. In that battle the Carthaginians, under the leadership of Hamilcar the son of Gisco, had defeated the tyrant of Syracuse, Agathocles. Agathocles had to retreat to Syracuse and lost control over the other Greek cities on Sicily, who went over to the Carthaginian side.
When Hamilcar besieged Syracuse and blockaded its port, Agathocles did not confront him on the field. Instead, he made the audacious but very risky decision to invade Libya, the homeland of the Carthaginians. He managed to escape the naval blockade and had some successes in his expedition to Libya. Hamilcar had to send a part of his army back to Carthage to reinforce Libya. In 310 BC a first assault on the walls of Syracuse failed.
In 309 BC, Hamilcar attacked again in the cover of night to obtain the element of surprise. His advance on the walls was made in disorder however, and the Carthaginians were in turn surprised by a counterattack from the Syracusans. Even though the Carthaginians heavily outnumbered the Syracusans, the element of surprise, the darkness of night and the terrain made the Carthaginian army flee. Hamilcar was captured and killed by the Syracusans. The naval blockade was finally broken in 307 BC by Agathocles himself, when he had temporarily returned to Sicily.
Prelude
The armies of Hamilcar and Agathocles clashed in the Battle of the Himera River in 311 BC. Agathocles suffered a disastrous defeat, a large part of his army was killed or taken prisoner by the Carthaginians. He gathered the survivors, burned his camp and withdrew to Gela. There he remained for some time to divert the Carthaginian army from Syracuse. This allowed the Syracusans to harvest their crops. Hamilcar first besieged Gela, but gave up when he discovered that Agathocles had large supplies and enough soldiers to defend the city. He then visited the cities and strongholds which were still siding with Agathocles to win them over. Because they despised Agathocles they soon deserted to the Carthaginians.
As the siege of Gela was lifted, Agathocles escaped to Syracuse with the remains of his army. He supplied the city with the grain harvest from the countryside and repaired the damaged sections of the city walls. He lost control over the rest of Sicily, while Carthage had gained superiority in land and naval forces.
At this point the future looked bleak for Agathocles. With the odds against him, Agathocles decided against fighting the Carthaginian army on Sicily. In secret, he decided to pursue an unexpected and very risky invasion of Libya, the heartland of Carthage. By doing so he intended to divert Carthaginian military power from Syracuse. In Libya he wanted to incite the Libyan allies of Carthage to revolt and plunder the wealthy territory of Carthage. Also, his experienced army would have an edge over the Carthaginian forces there, which were not as battle-hardened as their forces on Sicily.
Siege
Agathocles appointed his brother Antander as the leader of Syracuse and left him an adequate garrison to defend the city. To prevent an uprising in Syracuse to take place during his expedition to Libya, he separated families so that one group would be left in the city and one group would join his invasion of Libya. Even if those who remained despised Agathocles, they would not be inclined to rebellion out of care for their relatives who were with Agathocles.
Because he needed money for his campaign, he took the property of orphans, borrowed from merchants, took dedications from temples and the jewels of the women. He invited the wealthy citizens, who most opposed his rule, to leave the city voluntarily. As they left, he sent his mercenaries to kill them. He then seized their property and freed their slaves who were fit for military service. In this manner he gathered a large amount of wealth.
Agathocles departs to Libya
The Carthaginians were blockading the harbor of Syracuse with a fleet of triremes which greatly outnumbered the sixty ships of Agathocles had manned. Agathocles had to wait for a suitable opportunity to leave Syracuse. This moment came when a few grain ships en route for the harbor of Syracuse arrived. When the Carthaginian fleet temporarily lifted the blockade to chase the grain ships, Agathocles quickly led his fleet out of the port.