Excerpts from Books and Wikipedia
"Ad abolendam (...) was a decretal and bull of Pope Lucius III, written at Verona and issued 4 November 1184. It was issued after the Council of Verona settled some jurisdictional differences between the Papacy and Frederick I, Holy Roman Emperor. The document prescribes measures to uproot heresy and sparked the efforts which culminated in the Albigensian Crusade and the Inquisitions. Its chief aim was the complete abolition of Christian heresy." [Wikipedia] "This bull set up the organization of the medieval inquisitions." [Wikipedia: Timeline of Middle Ages]