Complex sentence: Further investigations conducted in 1920 resulted in the belief that the five stones found by Cortis were foundations of a wood watchtower, however, no further remains are visible nowadays because of long-lasting cliff erosion.
Split into simpler sentences: Further investigations conducted in 1920 resulted in the belief that the five stones found by Cortis were foundations of a wooden watchtower. However no further remains are visible nowadays because of cliff erosion.