Complex sentence: Reb Jehiel lived in Rome during the thirteenth and fourteenth centuries where he was a famous scholar, poet, copyist but was most well known as the author of the book of Piety Maalot ha-Middot.
Split into simpler sentences: Reb Jehiel lived in Rome during the thirteenth and fourteenth centuries where he was a famous scholar, poet, copyist. He was most well known as the author of the book of Piety Maalot ha-Middot.