Louis II, King of the Lombards and Emperor of the Romans, fought a five-year campaign against the Emirate of Bari, which fell in February 871.

The conquest of Calabria and assault on Salerno, the most important city in Campania, was the Aghlabid response to the fall of Bari.

The Salernitans had advanced knowledge of the attack by an arab called Arrane, which allowed them to make preparations and gather allies. In preparation for the siege, the city's defences were strengthened and the garrison reinforced. Troops came from the Lombard principalities of Benevento and Capua. Guaifer dispatched an embassy to northern Italy to ask the Emperor Louis II for aid.

The Aghlabid force under Abd Allāh crossed from Ifrīqiya (Africa), landed in Calabria and marched overland to Salerno, the Aghlabid army was considered very large. During its march north, it captured "many towns", It forced the Frankish army that was besieging Taranto, where the last remnants of the emirate of Bari were holding out, to abandon the siege.

In late fall or early winter, possibly as late as early 872, it laid siege to Salerno, which was too well defended to be taken by force. The countryside was ravaged to prevent food supplies from reaching the capital; its inhabitants either captured or slaughtered.

Deploying siege engines, the Aghlabids maintained a tight investment. In one of the earliest appearances of the word, the Chronicon Salernitanum calls these engines petraria. They were probably the traction trebuchets with which both sides would have been familiar. One particularly large one was used to slowly reduce a tower along the wall. According to the Chronicon Salernitanum, a certain Landemarius went over the walls and single-handedly destroyed it with an axe, killing many enemies in the process. In January 872, ʿAbd Allāh died and was replaced as commander by ʿAbd al-Malik.

On several occasions, the starving Salernitans considered surrendering. They were eventually reduced to eating cats and mice. After several months, Amalfi smuggled supplies to the defenders, this move was much debated in Amalfi, because "from the first it had made peace with the Hagarenes". After over a year of pleas and entreaties, Louis II, then at Rome, sent a Frankish army reinforced by Lombard contingents to relieve the siege. The Frankish force defeated an Aghlabid force near Capua on the banks of the Volturno, while a Lombard force defeated a separate detachment at Suessula. According to Andreas of Bergamo, there were 20,000 Saracens at Capua. The Frankish commander, Louis's nephew Cuntart, was killed in action. Following this, Louis II himself came south. At his approach, the Aghlabids abandoned the siege. According to the Chronicon Salernitanum, in the final week of the siege the Frankish army had marched using branches as camouflage and the besiegers had exclaimed "it is like a mountain comes against us".

Following their defeat, the main part of the Aghlabid army sailed directly to Sicily before returning to Ifrīqiya. Some bands, however, retreated to Calabria and others remained behind in Campania.

The siege of Salerno "represented the high point of Aghlabid involvement on the mainland". Following his victory, Louis II remained at Capua for a year trying to restore his authority in the south of Italy.

In the view of the Chronicon Salernitanum, the Aghlabids were God's avenging agents, sent to punish the Lombards for their betrayal of Louis II. Only after the Lombards had proved themselves faithful Christians and paid the penance of a siege, did God spare them. The chronicler compares the Salernitans to the ancient Israelites.

Florio handed the package into Guaiferio's hands, which immediately summoned the committee to consult it.

The council agreed with the prince that it was necessary to make substantial changes to the already mighty defensive belt of the city such as the raising of an anti-mural near the sea shore and the construction of three new towers (forts), two on the eastern side and one on the western one.

To rush to the aid of the prince, they welcomed Capuan workers who took care of the western side of the fortifications and Tuscanians who worked on the eastern side, Aldii and servants completed the necessary works by the spring of 871 just a few days before the arrival of the mighty fleet Saracen.

The prince of Benevento Adelchi was also present in the city with a small escort and when the enemies approached he abandoned the city to reach the seat of his principality, even the Capuans left the cities to take refuge in their city.

In the city, barricaded behind the fortifications, part of the Tuscians remained as well as the Salerno inhabitants in the vain hope that the gastaldi would bring in contingents of reinforcement.

Thousands of Saracens poured almost undisturbed on the beaches between Irno and Picentino under the leadership of the Emir Adb-Allah who immediately divided the troops into three contingents, laying siege to the city and the headquarters in the church of the Holy Martyrs Fortunato. Gaius and Ante to the east near the islet where the ships were moored (those who know Salerno know that today there is no islet but know Forte la Carnale in Torrione, the hill where the structure stands at that time it was an island a few meters away from the shore).

For several months the blockade was tightened, while the Saracens increased in number and received regular supplies, the besiegers instead began to suffer.

Suddenly the population of the city cried out for a miracle, the vault of the church of the Holy Martyrs collapsed, overwhelming Adb-Allah, but the exultation hard little, Abd-el-Melik, right arm of the dead Saracen took command of the expedition, the new agareno emir it was no less ferocious than the previous one.

It was decided to entrust the outcome of the war to a duel, Pietro brother-in-law of Guaiferio took to the field for the Salerno while a Saracen general was the opposing champion, the dispute took place in front of the church of SS Cosma and Damiano near Porta Rotese and was won by Peter but the Saracens did not keep their word and the siege resumed more bloody.

The besiegers had built a large mangle near a tower with which they threw huge boulders on the walls causing damage to the structure, a Salerno warrior, Landemario, descending from the walls during the night, managed to destroy the machine and killed the Saracens who guarded it, during his return to the city he was intercepted by a Saracen officer with whom he dueled victoriously.

Guaiferio, despite the acts of heroism and the strenuous defense, was aware that without an external military intervention he would not have been able to keep the city gates closed for long, he sent his son Guaimario I and his brother-in-law Pietro to the emperor Louis the Pious to ask for help, he instead imprisoned them and only later went down to Italy but to go to Rome to the Pope.

The months passed and the aid did not arrive, the Salerno people were forced to eat anything edible, including dogs, cats and mice, but a help in this sense managed to bring him Marino, Duke of Amalfi, managing to supply the city with provisions for by means of small boats that escaped Saracen controls.

The bishop Landolfo, knowing the city of Salerno to the end, tried to run for the cover of his Capua by sending an embassy to Ludovico who had meanwhile arrived in Rome with a strong contingent, the spies communicated the news to the emir who sent two columns of 10,000 soldiers each, one in Capua and the other in Benevento.

The Salerno people who were ready to surrender realized the weakening of the Saracen contingent, they opened the gates of the city and poured with the force of desperation on the enemies forcing them to take refuge on the islet and here too they were chased and beaten.

The survivors left the gulf abandoning 15,000 dead on the field, the other two contingents suffered the same fate, the one directed to Capua was taken from behind and annihilated by the troops of the emperor Ludovico who had rushed to defend the bishop Landolfo while those directed to Benevento crossed Adelchi's troops who managed to approach them with a rather imaginative stratagem.

The Chronicon Salernitanum reports a detailed description: “The Agarenes were settled in a place called Mamma. When the Beneventans saw the Agarenes, fearing that they would flee, they deceived them with a stratagem: they cut off all the branches of the trees and each with