Complex sentence: In the Byzantine period, the use of four arches with pendentives between them to support a dome allowed the spaces below domes to be opened up for lighting and for weight loads to be concentrated at just four points in a square, rather than circular, plan.
Split into simpler sentences: In the Byzantine period, the use of four arches with pendentives between them to support a dome allowed the spaces below domes to be opened up. Pendentives also allowed for weight loads to be concentrated at just four points in a square, rather than circular, plan.