218 BC

Second Punic War

Opening of the Second Punic War and Hannibal's Alpine crossing

Polybius says Hannibal's surviving troops looked more like beasts than men after the mountains — fifteen days in the Alps, at the end of a five-month march from New Carthage.

218 BC: a war declared, then a march

The year 218 BC holds two events that the old title fused into one. First came the diplomacy: after Saguntum fell, Roman envoys demanded that Carthage surrender Hannibal and his advisers or face war; Carthage refused, and the Roman delegation declared war. Whether Hannibal's attack had legally violated a treaty was itself contested — Carthage disputed Rome's reading of the Ebro agreement and Saguntum's status.

Only later in the year did Hannibal lead his army from Iberia through Gaul and over the Alps into the Po valley — territory of the Insubres in Cisalpine Gaul, not the Roman heartland. The war did not begin at the moment he crossed; Rome and Carthage were already at war.

Fifteen days in the mountains

Polybius puts the Alpine passage at fifteen days, at the end of a march from New Carthage that had taken five months. Which pass Hannibal used remains disputed — neither Polybius nor Livy gives an unambiguous route, and no decisive archaeological identification exists.

Polybius gives survivor figures: 20,000 infantry — 12,000 Africans and 8,000 Iberians — and no more than 6,000 cavalry reached the Po valley. His figures do not establish how many elephants completed the crossing. Hannibal halted at the foot of the Alps so his exhausted, underfed survivors could recover.

Rome splits its response

The consul Publius Cornelius Scipio, having failed to intercept Hannibal near the Rhône, returned by sea to Pisa to face the invasion — while sending his brother Gnaeus onward to conduct Rome's campaign in Iberia. One Roman expedition became two theaters because Hannibal had crossed the Alps.

Hannibal, meanwhile, had not abandoned Iberia to do it: he left Hasdrubal and forces behind. The immediate result was Hannibal's depleted army recovering in the Po valley, Gnaeus continuing the Iberian campaign, and Publius back in northern Italy.

Sources

Researched 23 Aug 2026 5 sources 3 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at -0218.

What the sources leave uncertain

No exact day can represent both the declaration of war and the Alpine crossing. The safest date is the year 218 BCE.
The precise Alpine pass remains disputed because Polybius and Livy do not provide an unambiguous route and no decisive archaeological identification exists.
Ancient accounts disagree over some marching figures. The verified numbers here are explicitly attributed to Polybius rather than presented as certain modern totals.
Whether Hannibal’s conduct legally violated a treaty was contested at the time: Carthage disputed Rome’s interpretation of the Ebro agreement and Saguntum’s status.