Complex sentence: The contemporaneous famous actors Thessalus and Athenodorus performed at the event, despite Athenodorus risking a fine for being absent from the simultaneous Dionysia festival of Athens where he was scheduled to perform (a fine that his patron Alexander agreed to pay).
Split into simpler sentences: The contemporaneous famous actors Thessalus and Athenodorus performed at the event. The actor Athenodorus performed despite risking a fine for being absent from the simultaneous Dionysia festival of Athens where he was scheduled to perform (a fine that his patron Alexander agreed to pay).