Adjacent to the library is the archive, which made the abbey famous. Founded in 1011 by S. Alferio, it quickly rose to great power due to the countless donations of goods, churches and monasteries by princes (especially Lombards and Normans), bishops and lords, as well as private individuals. The management, defense and claims of the various possessions and the administration of the lands given ad laborandum or in emphyteusis gave rise to a huge amount of documents, regests, inventories and land registers. The presence of documents prior to the foundation of the Abbey of Cava - more than six hundred - is explained by the fact that churches and monasteries were donated to the Abbey together with their archives. Among the most ancient monasteries are S. Massimo of Salerno (founded in 865 and passed to Cava in 1086), S. Maria de Domno also of Salerno (founded in 989 and donated to Cava in 1091) and S. Nicola de Gallocanta , between Vietri and Salerno, built in 983 and given to Cava in 1148. What has been said for the three monasteries also applies to other real estate - even modest ones - which became the property of the Abbey of Cava together with the relative documents.
Several archivist monks - with the title of vestararius first and then of armarius - since the century. XIII worked diligently in the custody, study and use of the documents, ordering them and noting the register on the back.
After the period of the commenda, with the aggregation of Cava to the Congregation of S. Giustina of Padua in 1497, archival studies also flourished thanks above all to D. Vittorino Manso, D. Alessandro Ridolfi and D. Agostino Venereo, undoubtedly the greatest archivist of Cava. The latter read and transunted all the documents, dividing them according to the funds and places of origin, separating the papal bulls and documents from the private documents, wrote on the back of each the summary with the chronological and archival data and transcribed these indications in large registers. At the same time, Fr Agostino recorded in various folio books all the information he considered interesting, creating still irreplaceable dictionaries for the various historical researches. It should be clarified that the paper material remained united with the parchment one.
In 1626, new cabinets were set up, marked with letters for diplomas and numbers for private documents.
In 1760, with the demolition of the old church, the archive and library, which were located on it, had to change location. It appears, however, that the current rooms, equipped with elegant wardrobes and decorated with beautiful Pompeian ceiling paintings, were set up in 1784. At the time it was abbot D. Raffaele Pasca and archivist D. Salvatore De Blasi, meritorious for unpublished archival works and for the Series Principum qui Langobardorum aetate Salerni imperarunt (Naples, 1785).
A notable novelty came with the archivist D. Ignazio Rossi (1827-1831), who placed the documents in chronological order and separated the paper documents from the parchment ones.
After the suppression of 1866, the monks, who remained as custodians of the material requisitioned by the State, in addition to the ordinary commitments of custody and study, dedicated themselves to the publication of parchment documents in the Codex diplomaticus cavensis, in 8 volumes (precisely 1388 documents from 792 to 1065 ). Between 1887 and 1890 they compiled the alphabetical index by names and by subject of the 7760 paper documents.
The archive has over 15,000 Latin parchments, of which the oldest is from 792, and 101 Greek parchments.
Not all Latin parchments have always been part of the archive. In 1807, about 1500 parchments from the Certosa di Padula, along with six codices, were purchased in Salerno (they were sold in the square to the first bidder) by the archivist D. Luigi Marincola, who thus saved them from dispersion. Around 1820 there were other 114 parchments from the convent of S. Francesco di Eboli and about 500 from the Celestini of Novi Velia. In the 1900s, for various donations, about 150 parchments were acquired: 122 from the Basilian monastery of S. Maria di Materdomini paid in 1924 by the Municipality of Nocera Superiore, 76 from Roccagloriosa donated by Baron Fernando de Caro in 1958, 49 from Capaccio donated by Dr. Vincenzo Rubini in 1975. Another 101 were recovered in the same year 1975 from the disassembly of the covers of notarial protocols.
The archival material was entirely studied by D. Agostino Venereo, who drew three fundamental works: Dictionarium Archives Cavensis in three volumes (copied in six volumes by D. Camillo Massaro), Additiones Archives Cavensis in three volumes; Familiarum libri in three volumes.
The chronological catalog of the parchment material, written in Latin, is contained in eight volumes in folio, one for the bulls and diplomas, the other seven for private documents.
In the archive there are regestas, inventories and census books of great interest. Noteworthy are: Regestrum D.ni Balsami Abbatis, years 1222-1225, in parchment; Inventarium abbatis Mainerii, 1341-1359, in pergpleasant; Liber reddituum et ecclesiarum Cavae D.ni Thomae Abbatis, 1261-62, in parchment; Regestrum D. Thomae abbatis, 1259-64, in bamboo paper; Regestra D. Maynerii (4 volumes), 1341-1365, in paper; Inventarium seu quinternus terrarum our monasteries S. Benedicti de Salerno antiquitus, sec. XIII-XIV; Inventory of S. Maria Maddalena di Bari, sec. XVI; Censi of the Vestarario, sec. XIV; Liber censuum Cavae, sec. XIV-XVI; Regestra D. Ioannis Cardinalis de Aragonia (5 volumes), 1475-1485; Libri visitationum (29 volumes), relating to the pastoral visits of the abbots of Cava from 1500 to 1934; 15 volumes of legal parchment copies of documents, bulls and privileges completed in the years 1503-1510; 182 volumes of notarial protocols ranging from 1468 to 1801; 155 administrative registers of the Abbey, from 1497 to 1853.
For the publication of the parchment material, some documents already entered the works of Muratori and Ughelli, but the complete edition was conceived after the suppression, precisely in 1869, by the monks of Cavensi, who published the Codex Diplomaticus Cavensis¸ edited by M. Morcaldi, M. Schiani and S. De Stefano, vol. I, Neapoli 1873; vol. II-VIII, Mediolani-Pisis-Neapoli 1875-1893; vol. IX-X edited by S. Leone and G. Vitolo, Badia di Cava 1984-1990. The documents published are 1669, from 792 to 1080.
Two funds merged into the archive for donation in the century XX: the Mansi estate, donated in 1970 by Miss Eleonora Mansi from Ravello, and the Talamo-Atenolfi-Brancaccio estate, donated in 1979 by the Talamo-Atenolfi-Brancaccio marquises of Castelnuovo Cilento. In 2012 the Prince Avv. Mario Putaturo Donati Viscido di Nocera, Deputy Chairman on. of the Supreme Court of Cassation, has entrusted the family archive, bound by the Superintendency of Naples, clarifying that it does not entrust it to the state library, but to the Benedictine Abbey of SS. TrinitĂ  di Cava, following the example of its Lombard ancestors.