Complex sentence: It was of basilica construction with a central nave separated by solid walls from the flanking naves, which exited into the transept, but did not communicate directly with the nave; its hemispherical apse was rectangular in its outer appearance.
Split into simpler sentences: It was of basilica construction, with a central nave separated by solid walls from the flanking naves. These exited into the transept, but did not communicate directly with the nave; its hemispherical apse was rectangular in outer appearance.