The long history of southern Italy in its various incarnations as the Kingdom of Naples and the Kingdom of the Two Sicilies—down through the swirl of Arabs, Normans, Germans, French and Spanish—is preserved in the State Archives.

The massive building that now houses the State Archives was originally the Benedictine monastery of Saints Severino and Sossio and is in the heart of the old city (photo, below), near the intersection of Via dei Librai ("Spaccanapoli") and Via Duomo. The monastery was one of the largest in the city and also one of the oldest, dating back to the 10th century. It was also known as the "cloister of the plane tree" as legend has it that the original building was erected in a grove of trees of that species (platanus), a specimen of which had been given to St. Benedict, himself. The history of the first few centuries of the monastery remains obscure; true enlargement of the premises started in the 1400s. Within the modern building are to be found works of art depicting the history of the Benedictine order.

The Second World War caused great damage to the archives, almost none of it from the unintentional ravages of war—accidental bombings, that sort of thing. (See Air Raids on Naples in WWII .) Most of it was gratuitous vandalism on a vast scale by the retreating German army as it left Naples in late September, 1943. It wasn’t even a "scorched earth" policy (since that has the strategic value of denying potentially useful resources to the enemy. “Scorched earth” would cover the German destruction of the port of Naples before they retreated; that was to render the largest port in Italy useless to the Allies. It didn’t work, by the way; Allied engineers had the port up and running in one week!) This was just book burning, plain and simple. It was mindless destruction of culture in order to “punish” Italy for surrendering to the Allies. The destruction extended even to incinerating a separate 200,000-volume collection of the Royal Society in Naples and setting fire to much of the Frederick II University of Naples, one of the oldest in Europe. Especially affected in the archives were documents dealing with Angevin and Aragonese history of the city—that is, the 14th and 15th centuries. The vandals even destroyed archives that had been moved to Capua at the behest of Benedetto Croce to protect them from bombing.

In the absence of much original documentation, historians have had to rely on secondary sources, which is to say the later Spanish and Bourbon documentation about the history of the city and kingdom as they found it when their turn came to rule. One thinks here particularly of such things as the detailed inventory of personal property and real estate in the kingdom undertaken by Charles III of Bourbon when he assumed the throne of Naples in the 1730s. Before that, some records survive of the Royal Chamber of the "Sommaria," a medieval commission that kept track of state expenses; as well, there are records of feudal inheritances.

Some records of the activities of the two centuries as a Spanish vice-realm survive, as well as the short-lived Austrian vice- realm in the early 1700s. Various sources exist, also, from the 1700s that document the rather complicated relationship between the Kingdom of Naples and the Vatican States. As well, there is documentation from the important French period under Murat and the introduction into the kingdom of the legal system known as the "Napoleonic Code," at least some of which remained intact even after the restoration of the Bourbon monarchy in 1815.

Since WW2, in order to compensate in some way for the wanton destruction of so many documents, attempts have been made to search out material in private hands locally as well as to bring back to Naples some of the documentation from abroad, such as the papers that the Bourbons took with them when they went into exile after the unification of Italy in 1861.