Complex sentence: In 1928, Rossi began his career at the University of Florence, as assistant to, In 1920, he founded the University's Physics Institute, which was located in Arcetri, on a hill overlooking the city.
Split into simpler sentences: In 1928, Rossi began his career at the University of Florence, as assistant to, who founded the University's Physics Institute in 1920. It was located in Arcetri, on a hill overlooking the city.