Complex sentence: There is still a question as to who built Portus Adurni, while some of the Saxon shore forts were built under previous commanders and emperors; some were built by Carausius during his revolt.
Split into simpler sentences: There is still a question as to who built Portus Adurni. While some of the Saxon shore forts were built under previous commanders and emperors, some were built by Carausius during his revolt.