 He tutored and mentored the sons of Casimir IV and postulated unrestrained royal power.In Kraków, the German humanist Conrad Celtes organized the humanist literary and scholarly association "Sodalitas Litterarum Vistulana", the first in this part of Europe.The folwark, a large-scale system of agricultural production based on serfdom, was a dominant feature on Poland's economic landscape beginning in the late 15th century and for the next 300 years.