 As was customary, Turin's defences were divided into the outer 'City,' containing the residential and commercial areas, and the 'Citadel' at its core.La Feuillade and Vendôme proposed digging trenches around the City at a distance of 300-400 metres, then blasting the Citadel into submission, an approach known as the 'Coehoorn method', after the Dutch engineer, Menno van Coehoorn.However, Victor Amadeus had significantly improved the Citadel's defences since 1696, using a design provided by Vauban, the French military engineer, and much of it was now underground.