In the artistic panorama of 17th and 18th century Portugal, the bishops are among the main actors whose patronage is still largely unstudied. In this context, we find people who were notable in their time for their enormous intellect and erudition. Among these figures is Dom João de Mendonça (1673-1736), the bishop who governed the diocese of Guarda for twenty-three years and seven months, and whose legacy is mainly associated with the Gardens of the Bishop’s Palace in Castelo Branco. Based on the analysis of the posthumous inventory (1736), and following the principle ‘tell us what you read and we will tell you who you are’, we will present the content of his extensive and valuable library, which reveals a man with a wide-ranging view of human existence.