Alboino was king of the Lombards from around 560 to 572. In 568 he led his ferocius people to conquer Italy, abandoning their native land, Pannonia. But lacking ships, they could not conquer the maritime cities, and in Campania many cities remained unharmed. This slowdown allowed to attenuate the ferocity of the invaders and to assimilate the Roman culture by the new Lombard generations.

Salerno was the last of the Latin cities that yielded to the invaders and, won but not defeated, it was given by agreement to the Sanniti Lombards (Benevento) only 76 years after the entry of Alboino, in 646 AD. Consequently, no ruin suffered, nor lost anything, and the palladium of the Latin civilization and of the Medical School could be preserved.

A long period of silence surrounded its events until the 8th century when it emerged from the oblivion of the written history and was defined "opulentissima" (exceedingly wealthy) by the historian of the Lombards, Paul the Deacon. Under the Lombard dukes Salerno enjoyed the most splendid period of its building development. The city, before the Lombard extensions, while towards the sea it ended with a wall coinciding with the southern limits of the monastery of San Giorgio and the princely palace, towards the north it did the same thing against a wall that ran latitudinally along the base of what will be the Plaio Montis.

 Seem  that, at the arrival of Arechi II. the city was not in the same prosperous conditions that the finds and sources of the Roman age seem to attest. From the words of Leone Ostiense, the intervention of the Lombard prince in Salerno takes the form of a sort of refoundation, leaving imagine a scenario of abandonment and decay of the urban structure: "Salernum quoque inter Lucaniam et Nuceriam antiquitus conditam mirifice restauravit "

The need to  find an outlet to the sea pushed Prince Arechi II towards the mid-8th century to reconsider the topographical picture of the Campanian dukedom strategically preferring the coast to the internal Samnite center of Benevento.

In 770 AD Arechi II decided to transfer the capital of the kingdom to the ancient castrum of  Salerno, in order to elude Charlemagne's offensive and to secure for himself the control of a strategic area, the centre of coastal and internal communications in Campania. Here Arechis, in addition to the fortification works, built a palatium using part of the structures of the Roman baths, which, celebrated by Paul the Deacon, will become the ultimate symbol of the power of the prince and later the symbol of the city in the Early Middle Ages. The re-foundation of the city of Salerno had a relevant role in shaping Arechis’s princely authority: he could represent his new political role in Southern Italy in a completely different framework. Arechis’s princely authority aimed to combine Lombard tradition with the local and even classical past.

Moreover, both Arechi II and Grimoald III entrusted Salerno – and not Benevento – with their family memory and prestige by both being buried in the cathedral. Following one of the most significant chronicles of Lombard southern Italy, the "Chronicon Salernitanum", during the 10h century the city of Salerno proudly retained not only the memory of the first dynasty but also that of the birth of the Lombard principality.

The fortification interventions continued with his son Grimoald III who erected a rampart (the “muricino”) to the south of the old maritime city walls, so the area between the two curtains of walls was called inter murum et muricinum, and then became an urban district. The following history of the city was marked by a gradual urban development and the birth of some quarters, such as the Jewish one called Giudaica, mentioned in the sources starting from the late 10th century.

During his reign, Sicardo fought repeatedly against the Saracens and neighboring cities, especially against Sorrento, Naples and Amalfi, and represented the greatest economic and military power in all of southern Italy. In 838 he managed to subdue Amalfi by attacking it from the sea, and deported several of its inhabitants to Salerno.

In 839 Prince Siconulf declared its independence from Benevento, turning Salerno into the center of a vast area with several districts (the gastalds): Salerno becoming the capital of a flourishing principality stretching out to Capua, northern Calabria and Puglia up to Taranto. The Lombard Principality of Salerno was formed in 851 AD.

The siege of Salerno was one of the campaigns of the Aghlabids in southern Italy during their conquest of Sicily. The Lombard city of Salerno had strong defences and, despite the use of stone-throwing artillery, the siege lasted a little over a year from its beginning in late 871 or early 872. Prince Guaifer of Salerno led the defence, but the siege was only lifted by the arrival of an army of Lombards and Franks under the Emperor Louis II.

In the summer of 928, an Arab expeditionary force led by the Slavic Sabir returns and, after capturing some enclaves on the Tyrrhenian coast, sails into the harbor  of Salerno, and forces the duke to pay an enormous sum of tribute (money and silk fabrics) to go away.

Around the year 1000 prince Guaimar IV annexed Amalfi, Sorrento, Gaeta and the whole duchy of Puglia and Calabria, starting to conceive a future unification of the whole southern Italy under Salerno's arms. The coins minted in the city circulated in all the Mediterranean, with the "Opulenta Salernum" wording to certify its richness. At the time of Guaimario - stated Salerno prelate, Alfano I (1058-1085) in carme "Ad Guidonem Principis Salernitani fratrem" - all the Southern Italy and its lineages, from Liri to Reggio, were subjected to Salerno and the city appeared more splendid and powerful of imperial Rome.  Salerno shone not only for its military power, but also for its wealth and cultural vivacity, rich in treasures from trade with the East and famous for its note “School” of medicine and surgery

Alfanus I was the archbishop of Salerno, translator, theologian, and physician. He was a key figure in medieval literature and science.

At the end of the 11th century Salerno was truly the most important city in Southern Italy. The largest Jewish community in Southern Italy was located in Salerno, and this presence left traces in the culture and topography of the city. However, the stability of the Principate was continually shaken by the Saracen attacks and, most of all, by internal struggles.

In 1056, one of the numerous plots led to the fall of Guaimario. His weaker son Gisulf II succeeded him, but the begin of the decline for the principality had begun. In 1076 Roberto il Guiscardo, brother-in-law of Gisulfo, besieged Salerno. The city was conquered due to starvation after eight months and the principality passed under Norman rule. Gisulfo II, the last Lombard prince, took refuge at the papal court of Gregory VII, and then spent the last period of his exile in the castle of Sarno, where he died (1090-91) cared for by his sister, the countess Gaitelgrima. In 1077 Salerno reached its zenith but soon lost all its territory to the Normans.