Complex sentence: It has an elliptical arena, surrounded by tiered seating for around 15,000 spectators, divided according to the requirements of Augustan ideology; the lowest seats were reserved for the highest status spectators.
Split into simpler sentences: It has an elliptical arena, surrounded by tiered seating for 15,000 spectators. The seating is divided according to the requirements of Augustan ideology, with the lowest seats reserved for the highest status spectators.