Complex sentence: By this time the grand inner harbor had silted up and was useless, however the Emperor Anastasius had reconstructed the outer harbor and Caesarea remained an important maritime city, providing the Persian Empire with access to the Mediterranean Sea.
Split into simpler sentences: By this time the grand inner harbor had silted up and was useless. However the Emperor Anastasius had completed a reconstruction of the outer harbor, consequently Caesarea was an important maritime city, providing the Persian Empire with access to the Mediterranean Sea.