Complex sentence: Although its archaeological importance has been known since the 1950s, when ploughing turned up sherds of Roman samian ware, it has not been subject to archaeological excavation, but numerous artefacts have been dug up by illegal metal detectorists.
Split into simpler sentences: Although its archaeological importance has been known since the 1950s, when ploughing turned up sherds of Roman samian ware. It has not been subject to archaeological excavation, but numerous artefacts have been dug up by illegal metal detectorists.