Meanwhile, Hannibal assembled a Carthaginian army in New Carthage (modern Cartagena) over the winter, marching north in May 218 BC he entered Gaul to the east of the Pyrenees, then took an inland route to avoid the Roman allies along the coast. Hannibal left his brother Hasdrubal Barca in charge of Carthaginian interests in Iberia. The Carthaginians crossed the Alps with 38,000 infantry and 8,000 cavalry in October, surmounting the difficulties of climate, terrain and the guerrilla tactics of the native tribes.