The Roman historian Titus Livius or Livy (59 BCE - 17 CE) is the writer of the authorized version of the history of the Roman republic. Many of the 142 books of the History of Rome from its beginning are now lost; however, we do have an excerpt, the Periochae. In books 12-14, he described the war against Pyrrhus, in which the Romans conquered southern Italy. The Periochae were translated by Jona Lendering; the Latin text can be found here.
Rome versus Pyrrhus
From book 12
[Per.12] When the Tarentines looted a Roman fleet and killed its commander,note[282 BCE.] the Senate sent them envoys to complain about this injustice, but they were maltreated. Therefore, war was declared.note[281 BCE.]
The Samnites revolted.note[The Samnites lived east of modern Naples, in the mountains. They were a powerful coalition of tribes, and the Romans had found it difficult to subdue them. Now, they sided with Tarentum and Pyrrhus.] In several battles, many commanders successfully fought against them and against the Lucanians, Bruttians, and Etruscans. King Pyrrhus of the Epirotes came to Italy to support the Tarentines.note[280 BCE.]
When a legion from Campania, commanded by prefect Decius Vibullius, was sent to Rhegium, it killed the inhabitants and occupied the city.
From book 13
[Per.13] Consul Valerius Lavinius unsuccessfully fought against Pyrrhus,note[280 BCE; the battle of Heraclea.] especially because the soldiers were not used to the elephants and were terrified. After the battle, Pyrrhus inspected the bodies of the Romans that had fallen during the fight and noticed that they were all directed against their enemy. Pillaging the country, he proceeded to the city of Rome. The Senate sent Gaius Fabricius to Pyrrhus to negotiate the return of the prisoners-of-war. In vain, the king tried to persuade him to abandon his country. The prisoners were released without payment. Pyrrhus' deputy Cineas was sent to the Senate to organize the king's entrance into the city to negotiate a peace treaty. It was decided to discuss this matter with all senators, but Appius Claudius (who had not visited the deliberations for a long time because he suffered from an eye disease) came to the Senate and persuaded the senators with his speech not to give up. [...] For the second time, the Romans fought unsuccessfully against Pyrrhus.note[279 BCE. The battle of Ausculum.]
The treaty with the Carthaginians was renewed for the fourth time.
When consul Gaius Fabricius heard from someone who had fled from Pyrrhus, that he could poison the king, he sent him back to the king with an indictment. [...]
From book 14
[Per.14] Pyrrhus went to Sicily.note[279/278 BCE.To attack the Carthaginians in the western part of Sicily. Go here for a description of this war.] [...] When consul Curius Dentatus was recruiting an army, he sold the possessions of a man who had not appeared. He defeated Pyrrhus, who had returned, and expelled him from Italy.note[275 BCE. The battle of Malventum, later called Beneventum.] [...]
A Carthaginian navy brought help to the Tarentines, and broke the treaty.note[272 BCE.]
It [book 14] also contains accounts of successful wars against the Lucanians, Bruttians, and Samnites, and of the death of king Pyrrhus.note[272 BCE.]
From book 15
[Per.15] When the Tarentines had been subdued, they were given peace and freedom.note[272 BCE.]