Complex sentence: Earlier collections of canon law had been codified in the "Decretales Gregorii IX", published under the authority of Pope Gregory IX in 1234, but in the succeeding sixty years, numerous legal decisions were made by one pope after another.
Split into simpler sentences: Earlier collections of canon law had been codified in the "Decretals", published under the authority of Pope Gregory IX in 1234. But in the succeeding sixty years, numerous legal decisions were made by one pope after another.