Picking the best from a 30m-strong archive

How can you even try to describe a place that aspires to contain all universal knowledge in just a few words? It is simply not feasible. But it is, perhaps, possible to gauge the value of Spain's National Library, the Biblioteca Nacional, through a few of the precious items in its holdings. A new exhibition, inaugurated on Tuesday by the king and queen, underscores the importance of the institution, which was founded 300 years ago by Philip V.

Given that the Biblioteca Nacional holds 30 million documents - including one of the world's most valuable collections of incunabula, extremely rare books printed before 1501 - choosing 240 items to illustrate the institution was not an easy task.

The show's commissioner, Complutense University professor José Manuel Lucía, spoke of "the sadness" he felt at having to discard so many other valuable items from display. The following are a few of the treasures of humankind that will be on view at the exhibition, titled 300 años haciendo historia (300 years of making history).

Commentary on the Apocalypse by St Beatus of Liébana. Just one of the 25 surviving copies of the original manuscript by the eighth-century monk from the Asturias region, in northern Spain. This particular copy arrived at the Spanish National Library when the nobles who had supported Carlos, the challenger to the Spanish throne, had their assets seized.

Cantigas de Santa María (13th century). The great work attributed to Alfonso X the Wise survives through four codices, detailing the Canticles of the Holy Mary - more than 420 poems with musical annotations that constitute an invaluable compendium of medieval religious music. This particular copy once belonged to the Toledo Cathedral.

Dante's Commedia (14th century). A copy of Dante Alighieri's famous Divine Comedy, originally known simply as Commedia, and containing high quality miniature illustrations. It once sat on the shelves of the personal library of the Duke of Osuna.

Ptolemy's Cosmographia (15th century). This item is made up of eight volumes, containing the work of the Greek mathematician and geographer who was rediscovered during the Renaissance.

Sgrooten's Atlas (1592). A cartography gem. Two manuscripts are known to exist, one in Brussels and the other at the Spanish National Library - the latter includes a handwritten dedication for King Philip II. The Atlas contains 38 large maps.

Drawings by Velázquez (17th century). The Biblioteca Nacional conserves four of the six existing drawings attributed to the painter from Seville, including two pencil portraits of a little girl and a young woman. The exhibition also features drawings by Goya, Murillo, Carducho and Fortuny.

Death of the Virgin, by Rembrandt (1639). One of the painter's most famous etchings, a technique he began using during his stay at Leiden.

Goya's Caprichos (1799). A collection of 80 prints on copper plates, whose mission was to moralize and censor human vice. Each print has an ironic caption underneath.

La verbena de la paloma, by Tomás Bretón (1894). Purchased by the Biblioteca Nacional in 1999, this is the handwritten score of what may well be the most famous zarzuela ever written. Also on display is the musical score for Concierto de Aranjuez, by Joaquín Rodrigo (1940).

Gyenes e Ibáñez. The archives of two of Gran Vía's best-known photo studios are kept at the National Library. The shots include an autographed portrait of Gloria Swanson and a picture of Gyenes with Joan Fontaine. Other photographic work on display includes images from the Spanish Civil War by Capa, Centelles, Chim Seymour and the Cifra agency.

Diary in sonnets from the exile of Miguel de Unamuno (1924-25). A recent acquisition by the National Library. After being chased away by the dictator Primo de Rivera, the writer, professor and intellectual went into exile first in Fuerteventura, and then in Paris. His experiences are captured in the diary he kept.

Poems written in jail by Miguel Hernández. Purchased at auction in 2008, these two sonnets are written with pencil, possibly on toilet paper, and represent an emotional outlet for a poet who was battling feelings of helplessness after the Civil War.

El Aleph by Borges (1945). Purchased at a Sotheby's auction in London in 1985, the manuscript contains annotations by the author and a dedication to Estela Canto. Other originals include Cañas y barro by Blasco Ibáñez, a poem by Pablo Neruda illustrated by Federico García Lorca, El concierto de San Ovidio by Buero Vallejo, El doctor Centeno by Pérez Galdós and Viaje de Cristóbal Colón by Bartolomé de las Casas.