Complex sentence: Leading a strong patrol back to the fort they discover that the fort has been destroyed with one wall being obliterated and all the Legionnaires are dead; some, including Commandant Fronval, are found bound and executed.
Split into simpler sentences: Leading a strong patrol back to the fort they discover that the fort has been destroyed with one wall being obliterated and all the Legionnaires are dead. Some of the Legionnaires, including Commandant Fronval, are found bound and executed.