Complex sentence: In Mycenean times Sicyon had been ruled by a line of 26 mythical kings and then seven priests of Apollo, but after the Dorian invasion the city remained subject to Argos, whence its Dorian conquerors had come.
Split into simpler sentences: In Mycenean times Sicyon had been ruled by a line of twenty-six mythical kings and then seven priests of Apollo. After the Dorian invasion the city remained subject to Argos, whence its Dorian conquerors had come.