Complex sentence: Caesar claimed that the local tribes there had executed their most serious criminals by burning them alive in a huge man-shaped sculpture of woven twigs; for Shaffer, this was "the most alarming and imposing image that I had ever seen".
Split into simpler sentences: Caesar claimed that the local tribes there had executed their most serious criminals by burning them alive in a huge man-shaped sculpture of woven twigs. For Shaffer, this was "the most alarming and imposing image that I had ever seen".