The current site of the Isontina State Library was occupied by the Imperial-Royal State Gymnasium (Staatsgymnasium) from the mid-nineteenth century.

In this school, also attended by Slovenian and Croatian students, the philosopher Carlo Michelstaedter completed his initial education at the beginning of the twentieth century, together with his friends Nino Paternolli, Enrico Mreule and Biagio Marin.

The Isontina State Library also houses the "Carlo Michelstaedter Collection," comprising a significant collection of drawings, paintings, letters, and manuscripts. It was established in 1973 by order of Paula, the philosopher's sister.