Complex sentence: Alghero was designated as a diocesan seat in 1503 but construction work on the cathedral did not begin until the 1530; it was not opened until 1593, and not finished and consecrated until 1730.
Split into simpler sentences: Alghero was designated as a diocesan seat in 1503 but construction work on the cathedral did not begin until the 1530s. It was not opened until 1593, and not finished and consecrated until 1730.