The Battle of the Bagradas River (the ancient name of the Medjerda), also known as the Battle of Tunis, was a victory by a Carthaginian army led by Xanthippus over a Roman army led by Marcus Atilius Regulus in the spring of 255 BC, nine years into the First Punic War. The previous year, the newly constructed Roman navy established naval superiority over Carthage. The Romans used this advantage to invade Carthage's homeland, which roughly aligned with modern-day Tunisia in North Africa. After landing on the Cape Bon Peninsula and conducting a successful campaign, the fleet returned to Sicily, leaving Regulus with 15,500 men to hold the lodgement in Africa over the winter. Instead of holding his position, Regulus advanced towards the city of Carthage and defeated the Carthaginian army at the Battle of Adys. The Romans followed up and captured Tunis, only from Carthage. Despairing, the Carthaginians sued for peace, but Regulus's proposed terms were so harsh the Carthaginians decided to fight on. They gave charge of the training of their army, and eventually operational control, to the Spartan mercenary general Xanthippus. In the spring of 255 BC, Xanthippus led an army strong in cavalry and elephants against the Romans' infantry-based force. The Romans had no effective answer to the elephants. Their outnumbered cavalry were chased from the field and the Carthaginian cavalry then surrounded most of the Romans and wiped them out; 500 survived and were captured, including Regulus. A force of 2,000 Romans avoided being surrounded and retreated to Aspis. The war continued for another 14 years, mostly on Sicily or in nearby waters, before ending with a Roman victory; the terms offered to Carthage were more generous than those proposed by Regulus. Primary sources The main source for almost every aspect of the First Punic War is the historian Polybius ( – BC), a Greek sent to Rome in 167 BC as a hostage. His works include a now lost manual on military tactics, but he is best known for his The Histories, written sometime after 167 BC, or about a century after the Battle of the Bagradas River. Polybius's work is considered broadly objective and largely neutral as between Carthaginian and Roman points of view. Carthaginian written records were destroyed along with their capital, Carthage, in 146 BC and so Polybius's account of the First Punic War is based on several, now-lost, Greek and Latin