The Collegium Hosianum was the Jesuit collegium in Royal Prussia, Poland, founded in 1565, 1566 by Cardinal Stanislaus Hosius in Braniewo (Braunsberg). The city of Braniewo was then part of the Diocese of Warmia (Ermland), a semi-autonomous part of Poland with cardinal Hosius as its prince-bishop. The Collegium Hosianum was one of the biggest Jesuit schools and one of the most important centres of Counter-Reformation in Europe and was particularly established to educate Catholic clergy of different countries.
The first Jesuits were called to Warmia by its cardinal Hosius, in order to counter the widespread Protestant movement in Prussia and elsewhere in Central and eastern Europe. The Jesuits arrived 2 November 1564. They were strongly opposed by the largely Protestant Prussian burghers and caused a religious split in the country. Despite difficult material conditions throughout the 16th century, they quickly founded many educational establishments: gymnasium (1565), convictus nobilium - school for Polish szlachta (1565), Diocesan Seminary (1567), Papal Seminary (1578) and dormitory for poor students (1582). The 16th century foundation was designed for 20 Jesuits, but the number soon approached 80, which resulted in problems with the finances of the schools and suitable number of school-rooms.
The Collegium was opened in a former Fransciscan friary. Renovation of the buildings was possible by funds given by Bishopric of Warmia. The Collegium was located in the western part of the building, convictus in the northern, and in the eastern part was located a school. In the first years the gymnasium was not very big due to lack of classrooms. There were five standard "classes" (courses) in it, of which the lowest was "infirma", and the highest was "rhetoric". To the initial problems of the schools were added boycotting by the Protestants and some fights between German and Polish students.
The Collegium in Braniewo distinguished itself from the other Jesuit schools in Poland and all of Europe with a specific curriculum: from 1566 there were taught German language, mathematics, singing and dialectic apart from standard subjects. After opening of the Diocesal and Papal Seminary some theological courses were introduced, and in 1592 also philosophical courses, which was a sign of the high reputation of the school. The school was elite and the number of students was not high, fluctuating from 130 to 300. The Collegium had an international character; besides local Germans, students came from all over Europe, with the majority of Poles, since the 1580s Swedes and Ruthenians added by Antonius Possevinus.