The death under mysterious circumstances of Tiberius Claudius Caesar Britannicus, heir to the Roman Empire, on the eve of his coming of age clears the way for Nero to become Emperor.

AD 55 (LV) was a common year starting on Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Caesar and Vetus. The denomination AD 55 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Tiberius Claudius Caesar Britannicus, usually called Britannicus, was the son of Roman Emperor Claudius and his third wife, Valeria Messalina. For a time, he was considered his father's heir, but that changed after his mother's downfall in 48, when it was revealed she had engaged in a bigamous marriage without Claudius' knowledge. The next year, his father married Agrippina the Younger, Claudius' fourth and final marriage. Their marriage was followed by the adoption of Agrippina's son, Lucius Domitius Ahenobarbus, whose name became Nero as a result. His stepbrother would later be married to Britannicus' sister Octavia and soon eclipsed him as Claudius' heir. After his father's death in October 54, Nero became emperor. The sudden death of Britannicus shortly before his fourteenth birthday is reported by all extant sources as being the result of poisoning on Nero's orders; as Claudius' biological son, he represented a threat to Nero's claim to the throne. In Suetonius' The Twelve Caesars, he claims that Nero poisoned Britannicus out of envy of his voice, due to Nero's own obsession with performance and being the best entertainer of all time.

The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Romans conquered most of this during the Republic, and it was ruled by emperors following Octavian's assumption of effective sole rule in 27 BC. The western empire collapsed in 476 AD, but the eastern empire lasted until the fall of Constantinople in 1453.

Nero Claudius Caesar Augustus Germanicus was a Roman emperor and the final emperor of the Julio-Claudian dynasty, reigning from AD 54 until his death in AD 68.