Quebec served as the only fortified city in the Americas, centred on the Citadelle of Quebec. An unusual feature of Montreal's defence was a string of 30 outlying forts to protect against the constant Iroquois threat to the expansion of French settlements. The majority of these were simple stockades, but as artillery was not as developed as on the battlefields of Europe, some of these were built like the fortified manor houses of France. Roughly four of these were substantial stone forts which served as defensive residences, sometimes considered "true castles", as well as imposing structures to prevent Iroquois incursions. Initially, Fort Senneville was a French stockaded fort, built in 1671 about half a mile above the Sainte-Anne rapids. The property was part of a fief ceded to Dugué de Boisbriant in 1672 by the Society of Saint-Sulpice, and subsequently relinquished in payment of a debt to two of the most significant figures in New France's history: Jacques Le Ber and Charles Le Moyne, who used the site as a fur-trading post.