Thesaurus SJ aims to grant the scientific community access to the unpublished collection of documents (from the 16th, 17th, and 18th centuries), unveiled during the restoration of the New Cathedral of Coimbra (formerly the College of Jesus). This collection was clandestinely preserved there since the days preceding the expulsion of the Jesuits in 1759.
It contains four sections:
- 16th-century documents (including letters penned by Ignatius of Loyola, Polanco, Francis Xavier, King João III, etc.)
- a Manuscript authored by Fr. António Vieira, Clavis Prophetarum
- a 17th-century volume, religiously and philosophically controversial
- letters and other 18th-century documents, including a historiographic notebook.
These documents have remained hidden for over 250 years, waiting to be brought to light.