In the 9th century, Arab forces arrived in Italy. The Byzantine Empire lost control of Sicily, because the commander of the island's fleet, Euphemius, rose in revolt against the Byzantine Emperor Michael II. Defeated by loyalist forces and driven from the island, Euphemius sought the aid of the Arabs in North Africa. The Arabs took Palermo in 831 and Syracuse in 878. By 902, the conquest was complete. The Emirate of Sicily was the first Muslim state in Italy.
In 841, Muslim forces captured Bari (on the Italian mainland) and established the Emirate of Bari, which constituted the second Muslim state in Italy. The first ruler of Bari was Khalfun, a Berber leader who had probably come from Sicily.
In 846, an Arab army sacked the suburbs of Rome itself including the basilicas of Old Saint Peter's and saint Paul outside the walls, although they did not enter the Aurelian wall.
The Duke of Naples and Prince of Benevento soon began a tradition of hiring Saracen mercenaries. Meanwhile, Arab-Berber fleets dominated the Tyrrhenean sea (west coast of Italy). In 849, an Arab fleet attacked Ostia (the port of Rome), although on this occasion they were defeated.
The Saracen camp at Minturno (in modern-day Lazio) by the Garigliano river became a perennial thorn in the side for the Papacy and many expeditions sought to get rid of them, although the Saracens remained undefeated until 915.
Given all this activity, was an Arab-Berber conquest of mainland Italy possible? They already held Sicily and much of the south, and it seems Rome itself was under serious threat. How plausible was an Arab conquest of Italy?