Excerpts from Wikipedia:
The city was established in 177 BC by Publius Aelius, Marcus Aemilius Lepidus and Gnaeus Sicinius Located at the mouth of the Magra, it was a military stronghold for the campaigns against the Ligures. An inscription of 155 BC, found in the forum of Luna in 1851, was dedicated to M. Claudius Marcellus in honor of his triumph over the Ligurians and Apuani. In 109 BC it was connected to Rome by the Via Aemilia Scauri, rebuilt in the 2nd century AD as the Via Aurelia. It flourished when exploitation of white marble quarries in the nearby Alpi Apuane and neighboring mountains of Carrara, which in ancient times bore the name of Luna marble.. Pliny speaks of the quarries as only recently discovered in his day; they were soon owned by the imperial family. Pliny the Elder considered the big wheels of cheese from Luna the best in Etruria. Good wine was also produced.
It derived its importance mainly from its harbour, which (according to the 1911 Encyclopædia Britannica) was the gulf on the Tyrrhenian Sea now known as the Gulf of Spezia or La Spezia Gulf, and not merely the estuary of the Macra as some authors have supposed. While the town was apparently not established until 177 BC, when a colony of 2000 Roman citizens was founded there, the harbour is mentioned by Ennius, who sailed from there to Sardinia in 205 BC under Manlius Torquatus. It was also being contested by the Romans as early as 195 BC, who were fighting the Ligurians and Apuans in the area.
The site was used as a base for the quarrying of marble from the marble quarries of modern-day Carrara, as the marble in that quarry is fine, and the harbour allowed the marble to be shipped to Rome easily.
In the 5th century, it was still notable, as it was chosen as the seat of a bishopric. Captured by the Goths in the following century, it was reconquered by the Byzantines in 552, who however lost it to the Lombards in 642. The latter damaged the city’s economy, favouring the trades routes that passed through the nearby port of Lucca to the south. Luni had been reduced to a small village by the time of the Lombard king Liutprand. Later, it was a countship and see under Charlemagne, exactly on the border between the Kingdom of Italy and the Papal States.
It was repeatedly sacked by sea pirates, Saracens in 849 and Vikings in 860. Luna is supposed to have been mistakenly sacked by the viking leader Hastein, who thought it was Rome. He tricked his way in by pretending to be a dying Christian convert. 9th century Bishop Saint Ceccardo is celebrated on June 16.