Complex sentence: Bergen op Zoom was the chief work of the great Dutch engineer, Menno van Coehoorn, and believed to be impregnable d' Espagnac, Jean-Baptiste-Joseph Damarzit de Sahuguet.
Split into simpler sentences: Bergen op Zoom was the chief work of the great Dutch engineer, Menno van Coehoorn. It was believed to be impregnable d' Espagnac, Jean-Baptiste-Joseph Damarzit de Sahuguet.