[3] The construction of the building intended to house the Ghislieri college was undertaken in 1571 under the direction of Pellegrino Tibaldi, one of the greatest architects of the time, who followed the works until 1585, the year in which he was called to Spain by Philip II.

The oratory, with a central plan, is surmounted by a dome with eight segments with a lantern; on the altar, the altarpiece of the Nativity, Saint Jerome and Pius V (about 1620), by Guglielmo Caccia, stands out.

[7] The constitutive bulls issued by Pius V did not foresee the existence of a library, even if in the College there were books owned by the institution, both bought directly from the founding pope, and forfeited when the abbey table of San Pietro in Ciel d'Oro was suppressed.

Among the privileged channels for enriching the book material there were acquisitions through bequests or donations, among which those of Pietro Ciapessoni, rector of the College and illustrious historian of Roman law, and Alessandro Pellegrini, Germanist and scholar of languages and European cultures.

The library now houses about 130,000 volumes: alongside textbooks freely for students, there are not only works of fiction and non-fiction, but also encyclopedias, repertoires and bibliographic tools for every area of knowledge.

The Ghislieri college has promoted and financed the restoration of the castle as a venue for multiple cultural activities: congresses and conferences, specialization and refresher courses, scientific seminars and exhibitions.