|Consul:||Ti. Sempronius Longus|
|Inf.:||4 legions + 20,000alae|
|Cav.:||1200 + 3800|
|Cav.:||6000 +37 elephants|
|Casualties:||? 36 elephants|
Battle at the Trebia
After P. Cornelius Scipio had crossed the Po he made his camp near the Trebia on the west bank. Hannibal, who had had to make a march of several days to find a spot where his army could cross the Po, was now nearing from the west and offered battle. Scipio, still wounded since the battle of the Ticinus, decided to move his camp to a better defendable place. He crossed the Trebia and moved stream up to the hills.
The river Trebia runs down from a spring in the Apennines and is fed by rain. Once in the Po plain it broadens and slows down. As visible on the picture (Google maps) it splits into several smaller streams in the same bed. This makes the river easy to be crossed there. Scipio had chosen position against the hills and Ti. Sempronius Longus who had been recalled from Sicily, built his camp near Scipio's. Hannibal took position on the west bank about 40 stades from Scipio's camp.
A lot of Kelts living in that area, were trying to play it safe, until it was clear which army was the strongest. When Hannibal sent troops to convince them with force, Sempronius saw his chance and attacked Hannibal's troops, who withdraw to their camp. Sempronius claimed a victory and was eager to start the decisive battle.
Hannibal chooses his battle field
Hannibal scouted the terrain and chose a space that met his needs for a successful battle. He had his brother Mago choose a thousand foot and a thousand horse and showed him a place to hide the next morning and from where to attack the Romans in the back on his signal.
The next morning he sent his Numidian cavalry to Sempronius' camp. They were to provoke the Romans and to lure them to the place where Hannibal's army would be waiting for them. It was still early and the Romans were still in their tents. When the Roman guard spotted the Numidians the alarm was sounded and soon Sempronius sent his cavalry out to attack them. Soon hereafter he dispatched his velites and then his full army. No one had a chance to eat a breakfast.
The Numidians kept retreating and attacking and lured the Romans through the Trebia and it's ice cold water. The Roman foot soldiers went in chest deep.
The battle order at the Trebia
Hannibal in the meantime had his troops prepare themselves and have a proper breakfast while staying warm near the fires. Then he moved his army about a kilometer towards the approaching Romans. Here he he positioned his army as shown in the diagram on the right. Polybius and Livius tell us he put the elephants on the outmost flanks, but to me that sounds illogical. The horse was to attack the Roman horse and would have left a considerable gap between the foot ad the elephants. Both writers claim the elephants were opposite to the Roman horse.
Sempronius positioned his troops very orderly and that took a lot of time. His soldiers were wet and cold, but he relied on his superiority in numbers. In foot soldiers that is, the Carthaginian horse outnumbered the Roman's by far and that would make the difference.
Between the two main powers were the light armed troops to screen them while taking position.
The battle of the Trebia
After some skirmishing by the light troops they withdraw through the main forces. At that same moment the Carthaginian horse attacked the Roman horse. It didn't take long before the Roman horse was defeated and chase off. After that the Carthaginians turned to the Roman flanks.
The Roman infantry was indeed much stronger than the Carthaginians and pushed them back. The appearance of the troops under command of Mago couldn't alter that.
Special trained Roman velites attacked the elephants. This was certainly not the first Roman encounter with elephants (Pyrrhus,1st Punic war) and they had developed adequate counter measures. They attacked them with spears until the animals turned around. Next the velites threw their spears into the backside of the elephant's knees. All but one elephants were killed.
The Roman infantry broke through the center rows of the Carthaginians, but their lines were smashes from the flanks towards the center by the Carthaginian cavalry. The centuries that broke through Hannibal's lines didn't know where to help and decided to bring themselves to safety. They marched right to Placentia. The others tried to flee through the Trebia. According to Polybius this river had now turned into a real obstacle that could no longer be crossed. I doubt that, though rain can change the character of this stream, it won't change that fast.
Who is to blame?
Polybius tries very hard to put the full blame on Sempronius and has Scipio warn him against this attack. But is is very well possible Scipio's army was involved too. A consular army in those days consisted of two legions not the four Sempronius used in this battle, so it is quite likely the other two came from Scipio. Always remember Polybius was a protege of the Scipios.