Complex sentence: A double line of fifteen-foot walls ringed the whitewashed compound, pierced on the waterside to permit the offloading of cargo from lighters, once merchantmen had passed inspection at an island further out in the harbour, where crews and cargoes were examined.
Split into simpler sentences: A double line of fifteen-foot walls ringed the whitewashed compound, pierced on the waterside to permit the offloading of cargo from lighters. Merchantmen were required to pass inspection at an island further out in the harbour, where crews and cargoes were examined.