Battle of Trebia (218 B.C.)Battle of Trebia (218 B.C.) - The first major battle of the Second Punic War on Italian soil (there was an initial skirmish at Ticinus).  It resulted in victory for Hannibal against a numerically superior Roman army under the command of Sempronius Longus.  Besides the defeat of Rome and the loss of about 20,000 of its soldiers, the major gain for Hannibal was that about 8,000 Celtic troops joined his army, which was one of his goals.  After losing so many soldiers crossing the Alps, Hannibal badly needed reinforcements in order to continue his campaign.  The Celts had been reluctant until his victory at Trebia.