Complex sentence: After this event Aegisthus reigned seven years longer over Mycenae, until in the eighth Orestes, the son of Agamemnon, returned home and avenged the death of his father by killing Aegisthus.
Split into simpler sentences: After this event Aegisthus reigned seven years longer over Mycenae. In the eighth year of his reign Orestes, the son of Agamemnon, returned home and avenged the death of his father by killing Aegisthus.