Complex sentence: The engineer responsible for the design and construction of the new fort was Josué Boisberthelot de Beaucours; he also oversaw major improvements carried out between 1718 and 1720 on the fort with modifications he felt would greatly increase the fort's defenses.
Split into simpler sentences: The engineer responsible for the design and construction of the new fort was Josué Boisberthelot de Beaucours. He also oversaw major improvements carried out on the fort between 1718 and 1720, modifications he felt would greatly increase the fort's defenses.